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FITS 2018 Tesla Model 3
ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit

ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit

Item # 119250KIT
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2018 Tesla Model 3

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ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit Plug and Lead 119250KIT
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2018 Tesla Model 3 wiring from Tekonsha. Product reviews from other Model 3 owners. Expert wiring advice with thousands of helpful questions and answers. Guaranteed lowest price and fastest shipping.
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2018 Tesla Model 3 - ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit

  • Trailer Connectors
  • Vehicle End Connector
  • 4 Flat
  • Plug and Lead
  • Tekonsha

Install a 4-way trailer connector on your Tesla Model 3 without cutting or splicing into your wiring. Zero-contact interface sensors identify the current flowing through each wire by simply clamping onto it. Circuit-protected module is made using SMT.


  • Provides a 4-way flat trailer connector at the back of your Tesla Model 3 to power your trailer's signal lights
    • Compatible with 5-pole, 6-pole, and 7-pole adapters (sold separately)
  • Bypasses factory wiring and involves no cutting, splicing, or plugging into Tesla Model 3's wiring
    • Sensors clamp onto the wires of your factory tail light wiring harness to detect current
    • No feedback, no interference with, and no power draw from your Tesla Model 3's wiring system
    • Easily removable and transferrable between different vehicles
    • Circuit tester included to ensure proper setup
  • Includes circuit-protected module that connects directly to car battery for power
    • Power wire, fuse holder, and 15-amp fuse included for installation
  • Works with 2-wire, 3-wire, PWM, and multiplex wiring systems
  • Constructed using surface-mount technology (SMT) for consistent, reliable performance
    • Maximizes trailer light yield and intensity while producing minimal heat
    • Ensures superior operation in rough road conditions
  • Comes with dust cap for 4-way flat connector


  • Application: Tesla Model 3s with 12V electrical systems
  • Maximum amperage:
    • Stop/turn lights: 4.2 amps per circuit
    • Tail lights: 7.5 amps per circuit
  • 1-Year limited warranty

This revolutionary wiring method makes it fast, easy, and safe to add a 4-way connector to your Tesla Model 3 so you can power your trailer's lights. Unlike traditional tail light wiring harnesses, which either splice into your vehicle's wiring or plug into designated ports in your factory harness, this system bypasses your Tesla Model 3's wiring entirely. Just clamp the intuitive sensors onto the individual wires of your OEM tail light harness and let the ZCI system do the rest.

Zero-Contact Interface Sensors


Each zero-contact interface (ZCI) sensor included with this harness is able to read the current that travels through the wire it is clamped onto. Upon sensing the specific modulation of that wire, a signal can be sent along the wire that connects the sensor to the included 4-way flat trailer connector. That signal is then transmitted through the connector to activate the appropriate function on your trailer lights.

Universal, Worry-Free Design

No Splicing, Cutting, or Connecting to Factory Wiring

Because the ZCI sensors can read the signals sent through your Tesla Model 3's wires just by clamping onto them, no cutting or splicing is necessary. The system completely bypasses all of your vehicle's wiring. As a result, your trailer's lights will be powered without overloading your Tesla Model 3's electrical system. And there is no chance of damaging feedback either.

When using this ZCI harness, you don't have to worry about voiding your warranty, nor do you need to be concerned about any potentially damaging errors on your part if you're not an experienced do-it-yourselfer. And if you have a Tesla Model 3 that doesn't allow certain modifications - like a leased car or truck - you can install this harness and remove it later with no obvious alteration to the Tesla Model 3.

Maximum Compatibility

This wiring harness is universal. You can use it on any vehicle that operates on a 12V, negative ground system. Because installation is so simple, you can easily remove the unit and transfer it to another car or truck at any time.

In addition, the ZCI sensors are able to read the signals sent by multiplex wiring systems and systems with pulse width modulation (PWM) and low-side-switched wiring, making the harness compatible with nearly all automotive wiring systems. This unit also works with both standard incandescent tail light bulbs and LED bulbs.

Built-In Tail Light Converter

Most trailers run on a 2-wire system - wherein the brake and turn signals are carried on a single wire. Many vehicles, however, are built with separate brake and turn signals. This type of system is referred to as a 3-wire system. If your vehicle operates on a 3-wire system, it will need to be converted so that it will be compatible with the wiring system of your trailer. This is done by adding a tail light converter to your wiring setup to combine the brake and turn signal functions of your automobile so that they run on a single wire to properly activate your trailer's tail lights.

This ZCI unit has a tail light converter built in to ensure proper functioning with any vehicle that operates on a 3-wire system. If your car has a 2-wire system and therefore does not need a converter, don't worry. The method of installing the sensors will take into account the wiring configuration of your vehicle so that only the necessary sensors are used, making sure the appropriate signals are sent back to the 4-way.


This universal harness connects to your Tesla Model 3's tail light wiring harness. To connect, just follow the included instructions. There are 4 ZCI sensors included. Each sensor has a colored label on it. Depending on your application, you will need to connect all or some of these sensors to the factory wires indicated in the instructions.

To get the power necessary to operate, the harness must be connected to a 12V power source. The included installation kit provides the hot lead required to connect this module to your car battery. When all connections have been made, connect the hot lead to the black wire on the ZCI power module and run the other end of the lead up to your car battery. Connect the hot lead to the included fuse holder, and then connect the fuse holder to the positive terminal on your battery. Then insert the included 15-amp fuse into the fuse holder.

Once installation is complete, the 4-way connector will be stowed in an out-of-the-way location either within your cargo area or beneath your vehicle, near the trailer hitch. If you choose to mount the connector near your hitch, a mounting bracket (sold separately) is recommended to keep the connector secure.

It is also recommended that you use a small amount of grease on all electrical connections on the 4-pole connector to help prevent corrosion.

Surface Mount Technology

Each ZCI wiring harness is built using surface-mount technology (SMT). This method of construction involves soldering electronic components directly to the surface of a printed circuit board. SMT eliminates the need for leads, which are used in older through-hole technology. The result is a circuit board that is smaller yet provides more routing area and that offers superior performance, reliability, and durability.

Circuit boards constructed using SMT have been shown to perform better under rough conditions with excessive vibration than those made using the through-hole method. And where would vibration be more likely to occur than in towing applications? SMT components also produce less heat, leading to increased durability and longer life. In addition, lower levels of resistance ensure better performance, especially for parts that operate at higher frequencies.

119251 Tekonsha ZCI Zero Contact Interface Universal ModuLite and Installation Wiring Kit

48705 LED Circuit Tester - 12 Volts

Installation Details 119250KIT Installation instructions

Video of ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Trailer Wiring Harness Installation - 2018 Tesla Model 3

Speaker 1: Today on our 2018 Tesla Model 3 you're going to be taking a look at and I'm going to show you how to install Tekonsha ZCI Circuit Protected Vehicle Wiring Harness with Four-Pole Flat Trailer Connector, part number 119250KIT. This is what our wiring looks like when it's installed. This wiring is going to live inside of the vehicle. It's going to give you all your proper lighting functions for your trailer. It's going to give you your brake lights, your running lights, both turn signals, and your ground.When not in use, you simply roll it up, and you can store it in an inside compartment inside the vehicle. When you're ready to use it, simply pull out what you need.

You're going to make sure you lay it over the rubber seal and stay away from any attachment points or connection points. While our wiring is outside of the vehicle, it is going to have an attached dust cap to cover all of your connections from any dirt, debris, and moisture.To start our installation, you're going to open the trunk of the vehicle. You're going to have a panel piece here. You're just going to pull up on it. You want to remove that.

On your driver's side, you're going to have three push pin fasteners. You're going to have one here. You're going to have one here, and then you're going to have one right up here. Go ahead and remove those, and you want to make sure that your felt is loose. On your passenger's side, you're only going to have two.

You're going to have one down here and you're going to have that one up there.Once you get those off, take your plug off the back of your light, and your light, the plug is going to be right in this area right here. How you take it off, you just push that tab. Then you go and pull it right off. Next you're going to have a little bit of coating. It's probably just a little bit of electrical tape.

Go ahead and pull that off your wires. Then what you're going to need to do is take your tester and I would suggest not probing the wires yourselves.What you're going to have somebody do is sit in there and turn on the left blinker and you're going to touch these little metal areas right in here, which is going to the wires. You're going to touch them and you're going to figure out which wire is your blinker and which one is your running light. Now, we've already tested them and determined that our purple wire is going to be our blinker on our driver's side or left blinker, and the red wire over here is going to be our running light signal.So once you determine those, write them down, and then you're going to test the passenger's side. Now, on our passenger's side we've tested and determined that our red wire is going to be our blinker or our right turn signal, and our yellow wire is going to be our running lights. So now that we have determined what our wire functions are, we're going to connect our ZCI plugs to our existing wiring. What's great about these is we don't have to splice into the wiring. We're just going to put our wire in there when we close this down and it reads the signal as it passes through.As you can see, every single one is marked. That's our taillight. We have our left turn signal, and then we have our stop or brake lights, and then we have our right turn signal or our passenger's side. All we're going to do is we're going to open this up. We'll pop that open and then this is for our taillights or running lights, which is going to be our red. All we do is we set our wire in there like this. Then we close that down on it. This is going to be our foam pad. We have one side that's going to be a sticky side. Peel that off, and we're going to wrap this around our plug like that.We'll do the same thing for purple wire, which is going to be our left turn signal. Make sure you get any other wires in there. You just have the wire that you are threading in. Then finally our stop. See how this arrow . This arrow means going out towards the light. So, you want to make sure you install that, this little cap here that will hold our wire in place, they're all going towards the plug. All right. We can go ahead and plug this back into our taillight. Then I'll bundle up that excess wire here real quick. Zip ties come in your kit, so I'm going to go ahead and mount my module here.In your kit you're going to get a piece of foam pad like this. It's double-sided sticky. Go ahead and peel one side off. Firmly press it into place, and then we'll find a place to mount this. Where I picked, there's actually a flat spot right here. I'm going to peel that off. That gives us plenty of room to mount our ground wire. We'll take a 10 millimeter socket and we'll go ahead and remove this bolt here. Add our ground wire, and then reinstall it.Now we're going to have our power wire that we're going to be running to the front of the vehicle to the battery, and it's going to come off of our power wire that's coming off of our modular box. We're going to add our butt connector. Then we'll add them two together. Then I'm going to wrap them up with a little bit of electrical tape. Now we'll have a couple fasteners, push pin fasteners we'll pull out. They're running across the back here. It's just going to make it a little bit quicker to get our wires ran across the passenger's side.I put my wire down in there and put my fasteners back in place. Now we can connect our other one to our right turn signal. To get our power wire up to the front of the vehicle, we have to find a way out. On our passenger's side, right down in here, there's actually a rubber grommet. You can see my black wire going through my grommet there. That grommet sits about right here in my fascia. So, what you have to do is you have to remove your taillight, which there's two eight millimeter bolts inside. Make sure you unplug the wiring, and then you pop it right out.There's a 10 millimeter bolt right on this top side of this in between the light and this top of the fascia here, right back in this corner. Down here in the wheel well, there's three push pin fasteners that run across the bottom, and then right up here up top there's a T25 Torx bit that holds your fascia to your fender. Once you do that, you can slightly pry out on this and pull it out enough to get to that grommet. All I did was cut a cross in it or X in it, pushed my wire through it, and you can see I've got it run right here.What I did is I took a 10 millimeter socket, removed a couple of these bolts here for this panel, just enough to pull it down, and what I got above my suspension there, there's a hard line. I took these down, and you can see I ran it right here, and this panel, it sits right up against the bottom of the car. I tucked it in all the way up to the front of the vehicle. I took this 10 millimeter bolt out. There's a push pin fastener that holds on this corner of this plastic piece I popped that down, fed it up through, replaced those, and you can see my wire comes right out of the front here.Now, this being an all-electric car, all of this is all the batteries and the power. So, the 12-volt battery is up in the front right underneath the windshield wipers. From right here, it goes straight up to it, and it's all pretty much open. This goes through the front trunk in the vehicle. What I did is I ran a airline tube down. I have my 12-volt wire. I just pushed it in the end. Now I'll go up top, and I'll pull that, and it will pull my line up.Up here in the front of the car, you're going to have a panel like this. It's going to sit just like that. All you need to do is just pull up. There's some little fasteners. You pull up, it'll pop off. Set that aside and you'll see this air intake here. Just kind of pull up on it like this. Pull just that top part out, and then we have our battery right here. This is my airline tube that came up from the bottom. There's my power wire. Now I can take that and connect it to the positive side of my battery.Now we'll strip back the end of our power wire. You're going to have a fuse holder in your kit that looks like this. Pull off one side. Go ahead and add your butt connector that comes in your kit, and the other end onto the power wire like that. For this end, you're going to have a ring terminal. There. Now take a 10 millimeter socket. Go ahead and remove this nut here on the top. We're going to make sure that the fuse is not in the holder when you put this on. Tighten that back into place. Now we'll take a heat source and we'll heat up our heat shrink butt connector that comes in our kit.Once your car is in run mode, all your functions are turned off. Go ahead and install your fuse. Then you're going to run through all the functions, and you're going to go in through each function and leave it on for five seconds. Now we'll test our wiring using part number I26. Running lights. Left turn. Right turn. Brake lights. Now we can reinstall the cover here. That'll do it for a look at and installation on the Tekonsha ZCI Circuit Protected Vehicle Wiring Harness with Four-Pole Flat Trailer Connector, part number 119250KIT on our 2018 Tesla Model 3.

Customer Reviews

ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit - 119250KIT

Average Customer Rating:  4.6 out of 5 stars   (188 Customer Reviews)

Install a 4-way trailer connector on your vehicle without cutting or splicing into your wiring. Zero-contact interface sensors identify the current flowing through each wire by simply clamping onto it. Circuit-protected module is made using SMT.

- 119250KIT
2016 BMW 3 Series

Installed in an afternoon, could have been under an hour with model specific instructions. The car ('16 BMW 328iX wagon) has a bulkhead connector through the passenger side rear quarter where all the tail light & other rear end wiring exits. That bundle of wires splits off a larger loom ~6" before the bulkhead, which looks to be the easiest spot to install the current sensors. It's tight access but also less than a foot away from the battery. It's all accessible by just pulling one interior panel, no need to touch the drivers side at all, installation at each taillight location doesn't make sense for this car. Oh yeah - both L & R turn signal wires are black/white, so you have to double check before buttoning things up. The product works perfectly as advertised. My only request would be for a little more streamlined shape to the sensors for tucking into a tight space like mine. 296467

- 119250KIT

Installed on 2018 Jeep Grand Cherokee Limited with no tow package. Install was kind of a P.I.T.A. But worth doing on your own to avoid the stealership. Not too much electrical knowhow required, as the black wire on Jeep tail lights are all ground. Running the power cable was the most difficult part, and required removing the interior rear quarter panel, which I managed to break a plastic clip. Would not recommend this on a Jeep, as there is no simple way to install this on the interior of the vehicle since the tail lights are wired 100% outside of the car. I’d say skip if you are looking into this for a Jeep, and wait for an OEM trailer harness to come out from mopar. 697887

- 119250KIT

I’m happier than I thought I would be with the results. Even the nifty little 12 V tester work fine. The instructions were more than adequate, there was plenty of wire and everything worked on the first try. 566365

- 119250KIT

The trailer hitch and wiring assembly have worked flawlessly. After calling several local installation outfits and receiving estimates of $2,000+ I decided to install myself. I have a little mechanical experience but this was the first hitch and wiring harness for me. This is my wife's X5 so I was a little nervous about popping rivets and pulling the rear bumper cover off, but eTrailer has excellent step by step video instructions by model year. The order included replacement rivets and detailed instructions. They could not have made this any easier. I really took my time and completed the job in about 5 hours. The final install looks professional and clean. The no-splice wiring harness is amazing - worth every penny. Tools: I was able to easily pop off the existing plastics rivets, and installed the new rivets (included from eTrailer) with pliers pretty easily - you may want to borrow a plastic rivet gun from your local hardware or auto parts store. On the X5 your have to cut a small notch out of the underside of the bumper cover. I happen to have a Dremmel which worked well. You may be able to use a razor blade. The plastic is not that thick. Pictures are attached. Thanks etrailer! 675332

- 119250KIT
2010 BMW X5

I selected this kit to install in my 2008 BMW X5 because I didn't have to splice into my vehicle's wiring and risk damaging something and it was extremely easy to install. It turned out to be even easier than I originally anticipated. Total install time was about 45 minutes start to finish. And even better, if I ever need to remove the kit from the vehicle, there won't be any trace that anything was ever installed. Difficulty level to install on a scale of 1 to 10 with 10 the most difficult is about a 2. Works perfectly as described. Highly recommend over any other trailer wiring kit available. 541233

I’ve been using this wiring harness now about a year to run several small trailers with no problems. I always check all trailer lighting afyer hooking up and no issues.
DougR - 07/13/2019


- 119250KIT
2015 BMW X5

Very well thought out product, no cutting or drilling required to install. The light kit is superb as well, loved the way it attaches to the wires and operates independently of the electrical system. Well done! 501262

- 119250KIT

Product was simple and straight forward to install on my BMW X6, however, it does have some issues. The lights are inconsistent at best. The lights on my travel trailer sometimes work perfectly and some times not. The issues are that sometimes the lights just go out while traveling down the road and then come back on minutes later or not at all. When the lights won't come back on I have to pull over, turn the car off and then restart. This works to bring the lights back on. Other times the trailer lights just stay on. Turn the car off and the lights just want to stay on. Unplugging them turns them off. So.......they work......sort of. I hope this helps. 463447

- 119250KIT
2013 BMW X5

Great product! I was able to install on my BMW X5 in less than an hour, very easy installation. I placed the order with Etrailer and while I awaited its arrival I watch the video associated with the installation. When the item arrived I opened the box verified I had all the required parts and made the installation without reading the instructions. Watching the video is invaluable and well worth the time. Upon completion I hooked to my trailer and it worked flawlessly. If you follow the set up you will have no problems. I liked the fact I had to do know splicing and removal should be simple. I ran my wiring to the hitch so I didn't have it hanging out the back hatch. When I looked online it suggested the removal of the bumper cover. I was able to run mine down behind the bumper and to the hitch with out removing anything. I simple fed it behind the bumper with the tailgate down. It tucked neatly behind the bumper and I zip tied it in place. The unit seems to be well built but is a little pricey in comparison to other units. The benefit of having a universal harness that requires no splicing with easy installation was the difference maker for me. 414075

- 119250KIT

The description of the product is accurate. The info on how to install is straight forward and well illustrated. I don't remember if this purchase had video support but I know other purchases from etrailer did. I've been very satisfied. The fact that this product doesn't violate the wiring should keep my vehicle warranty intact. 366909

- 119250KIT

The Tekonsha wiring harness was a bit difficult to install, as the clip-on connections are a somewhat bulky to fit in my Tesla Model 3's tight spaces. The good news is: they work as promised like a charm with our tiny camp trailer's lights. In truth, I have only had to use them once, but cannot imagine that any unforeseen problems would occur with them in the future. 671336

- 119250KIT
2008 Mercedes-Benz E-Class

I've towed racing sailboats for many years, mostly with European automobiles. Needed the hitch later this month so I could pick up a "new" one I just bought . This install was the second easiest out of the 6th I've done myself. High quality kit fits great. Even though Curt says the C11701 doesn't work on my 2008 Mercedes E350 4Matic Sedan Sport, I had absolutely no problems. The Tekonsha light converter was a snap too. Certainly lots better than the old days when I had to jury-rig the trailer lighting to match the car. Finally, your service was super. Couldn't be happier. Thanks! 395365

Very easy installation and zero problems since. Tows the new racing sailboat great. Highly recommended.
George S - 06/12/2018


- 119250KIT
2013 BMW X5

Bought the hitch and wiring harness from etrailer.com last year, and following their excellent video installation instructions, was able to complete the installation in only a couple of hours. (Would take about half that time to do it again, always worried about breaking something!) Everything has worked flawlessly, and we have been completely satisfied with the purchase and support. Will definitely return the next time we're in the market for hitch related products. 515249

- 119250KIT
2018 BMW X5

Excellent product delivered ahead of scheduled date. Fits well and fairly priced compared to other competitors 556184

- 119250KIT

Overall I am very happy with this product. It worked as advertised and wasn’t too hard to figure out. The one thing that would have given this item a 5 star rating would have been better directions. It would have been nice to have everything labeled step by step. For example, step one do this, step two do this. Etc. 661280

- 119250KIT
2018 Audi Q5

This harness works great, although it took a lot of repeated tries "learn" the module to my 2018 Audi Q5. My local specialty repair shop was willing to give this ZCI solution a try so they could offer it to future customers. They had done a cut-and-splice harness for a previous customer on the same model but were turning down further requests because they found the re-programming and recalibration of the electronics to be prohibitively complicated and time-consuming; even the AUDI dealers I called were balky and a little vague about the time, effort, cost, and warranty implications. My local guys found the installation easy but could only get it partially working at first. After multiple views of the video and exhaustive attempts to isolate the issue, it finally worked, for no apparent reason, on the 5th or 6th repetition of the "learn" routine. Despite those issues, I recommend this as being worth trying as perhaps the only reasonably-priced path to trailer wiring for this model. 556229

- 119250KIT
2012 Volkswagen Golf

The non-contact (ZCI) trailer light interface, though expensive at $180-plus, is exactly what my VW Golf Sportwagen needed. With its LED tail light system, the clamp-on sensors are the only thing that works. The only negative is that it took me a couple hours to carefully determine which contact pins are which signals. Then it took another couple hours to carefully route & dress the wiring. Contrary to instructions, I used the 12 v outlet in the rear and avoided fishing a power wire from the battery. It worked just fine! I ended up using the Left Turn Signal, Right Turn Signal, and the Tail Light Signal. The Stop sensor was unused. 567282

- 119250KIT

The TEKONSHA no contact wiring harness seems to be a very good product. I had it installed by the Hyundai dealer. This was a new product for them so I explained that it is probably the way of the future since it doesn't effect the factory wiring at all. They were also interested in trying it so only charged me for one hour of labor since they were also learning about the product. It has worked as advertised so far. I use it for auxiliary lights on my bike rack. The lights are LED so the draw is minimal. 680002

- 119250KIT
2014 Subaru Impreza

My mechanic and I have no concern that the product will perform well but there were some significant issues with installation that could be fixed with some careful attention. All wires on the unit are the same color and when the product arrived, all of the wire labels had fallen off. Determining each wires function was a painful and tedious process that took considerable time. That process is beyond the do-it-yourselfer. Also, the wire connection grommets seem to fall away from the wire when engaged. They had to be taped to the wire to prevent disengagement. We were able to work through these issues and the harness works perfectly. Either placing better wire labels or color coding the wires could prevent this problem in the future. As for the grommets, numerous potential fixes could be considered. 525133

- 119250KIT
2017 Land Rover Evoque

Well built wiring kit and good instructions. The Land Rover's wiring is tough to get at, but after taking the spare tire out and the fuse block door off I could get at them. One thing the instructions didn't indicate is that the rear lights appear that they have to be plugged before the module will learn them. Tried the first couple times with the connector removed from the light and the module would not work. Removed the fuse, but the tail lights back in and went through the learning process and it worked the first time. 430624

Working great and never had an issue with it.
Brian S - 09/10/2018


- 119250KIT
2015 Volkswagen Golf

When trying to get a trailer hitch and electrical wiring for my 2015 Golf Sportwagen, I was a bit frustrated by the response from VW -- on the one hand they stated in the manual that the vehicle was not designed to tow, but on the other hand they gave specification for a trailer, but the dealer was no help installing either a hitch or harness. So, I got the hitch from Torklift EcoHitch (a GREAT product), and after much searching, the 119250KIT from etrailer for the electrical. I had a service shop install the electrical (VW dealer would not touch it!), and it seemed to work fine for a year. I was a bit troubled by the mounting of the connector outside the car, using the supplied little harness. But, proceeded anyway. We had a pretty rough winter up here in northern UT, and when I went to connect my trailer for spring gardening work, the electrical connector was badly damage, with both corrosion of the contacts and bent contacts I had to straighten to get the thing to work. Message #1: Do NOT mount the connector outside the vehicle! I had the repair shop replace the connector, and when they did, they could not get the lights to work properly. Most important issue: even with the car totally off, when the trailer was plugged in, the left trailer tail light was on, and it ran the battery down! We determined that the problem was likely a fault in the power module. Note that the text on the module clearly states 'Circuit protected'. I am not sure what we did, but it is pretty clear we blew the thing. And, I could not get a replacement without buying the whole kit again. There was no option, either from etrailer, or Tekonsha (manufacturer of the module) to just get a replacement module. I feel a bit stuck, but lessons learned: I am NOT mounting the connector outside again, where it is exposed to road salt in winter, and can corrode, and I will be careful not to cause a short when making the connection. I will reserve final judgement on the 119250KIT for a year or so, if it does not fail again, I will be happy! 390291

- 119250KIT
2016 Lexus RX 350

I purchased and installed the 119250KIT in my 2016 Lexus RX 350- WITHOUT the factory trailer package. Although Lexus will always tell the consumer it Must have the factory wiring harness, it does not. I did not take pics but this is not a difficult task to accomplish. Be patient and follow these steps, it is about an hour long task. To install the wiring harness, first remove the plastic trim at the bottom of the lift gate, it is held down with plastic fasteners and simply pops off. I strongly suggest going to Harbor Freight and buy their $4 kit of plastic pry bars, rather than risk scratching up the paint on your vehicle. Next remove the deck storage buckets and carpeted pieces to left/right of the spare tire, this will allow you open access to the wiring. I installed the Tekonsha module on the driver's side in very back to left of the spare and on the back of the wheel well. Don't put on the double sided tape yet, this will be done in a later step. Next step is to remove the small plastic (3" x 2") vent on the rear left vertical carpeted wall, it just pops out from the bottom (first), then slide down, and off. Now, carefully remove the left tail light by using a plastic pry (from Harbor Freight) the whole assembly will slide out of the plastic snaps from front to rear. Use a towel when you let it 'hang' against your paint. There is a thin plastic cover piece which is in the lift gate track and covers 2 tail light bolts- which pops out easily. Once the assembly is removed, you will see the turn signals bulb insert has a colored (power) wire and a ground wire (twist this to unlock and allow you to test which wire is hot). The other wires on the assembly go to the running and brake lights- test them in a similar manner to determine which color is running lights and which is brake light. Look through the opening where you removed the 'vent' to see the tail light wires and pull/trace them by color into the back of the vehicle. You will have to slide the tail light wires (carefully 1 at a time) through the black water tight rubber plug to give you some length to clip on the Tekonsha connectors. I connected the Left, Running, and brake light -Teconsha clips all on the left side of the vehicle. Don't wrap the foam around them until they first test ok. All of the arrows on each Tekonsha clip should point toward the (rear) tail lights. A CRITICAL task is to locate a GOOD ground from the Tekonsha module (white wire) in the back of the vehicle. In my Lexus, under the Lift Gate area, I located a steel screw which already had 2 white wires with black stripes and extended the (short) Tekonsha to allow me to use this. Without a GOOD ground, you WILL have problems, waste a lot of time (1 hour plus), and aggravation to troubleshoot problems later. Trust me, I know!! Now that you have completed the wiring on the driver's side, do the same with the passenger side. Here you only need to run the single clip for the turn signal (1 wire). The Tekonsha clip is long enough to run across the lift gate area next to the factory harness. Locate the appropriate right turn signal wire by sliding off the right tail light similar process to the left light you just did. Clip on the Tekonsha clip. Next I tested all of the lights with my trailer. Once all were working, I put the foam wraps on each clip, secured the Tekonsha module using the double sided tape (on rear of wheel well), secured loose wires with zip ties, bundled together- all excess wiring, and secured in the side well. The last task is to run the black power wire from the Tekonsha module up to your battery in the engine compartment. If you are not too large, you can fit under the vehicle- otherwise raise it off the ground (safely) so you can get under the left side to route the wire. First, disconnect the negative battery cable from the battery post! Next, I loosened the 6 bolts which held the black plastic covers (under carriage of RX 350) and ran the wiring from just in front of the LR wheel all the way forward to my battery. Zip tie along the way as necessary, as not to interfere with moving parts. Then from under the vehicle, I ran the remaining wire around the LR wheel and zip tied again as not to allow any pinch points or abrasion (from suspension) of the wire. In the LR quarter panel of inside of vehicle you will see a rectangular brown plastic which will pop out and allow you access to pass wires from the undercarriage to the inside. This is where I ran the power (to battery) and trailer light 4 wire pigtail (to hitch area). Since it is plastic, I cut out a little square in the bottom of it and reinserted this in original place. Next, go to the front of the vehicle and install the fuse holder to the positive side of battery. Reconnect the battery ground and insert the 15 amp fuse provided. Give your system another check and verify the fuse did not blow. Put back the removed panels and pieces- you are all set to tow!! 278814

- 119250KIT
2015 Mercedes-Benz GLK-Class

everything as advertised as it should be. Not advertised was the excellent service and every attempt to get my product to me on a tight time schedule. Above and beyond, but just what I want to do for my clients. Really great service! 328643

Still working well!
johnR - 12/27/2017


- 119250KIT

The unit seems to be working, but it took about 8 hours to install, not the one hour the instructions say. The written instructions were, for the most part, useless. Thank goodness I was able to find a couple videos on YouTube that show how to install it. Only one of the wires were labeled as to which circuit they connect to (right blinker, brake, whatever), so I had to do trial and error. To top it off, the wires to the right blinker were about a foot too short, so I had to drive about 45 minutes to the nearest auto store, buy some wire, and then drive 45 minutes back! Two thumbs down on this product! 565366

- 119250KIT
2014 Audi SQ5

Took a while to figure out the wiring and testing, but I'm happy now. If you have a 2014 SQ5 and use the ZCI wiring harness, you'll need to connect the following wires (and make sure to have the tailgate closed when testing): Driver Side Black w/ Blue Wire to Lights Grey w/ White Wire to Left Turn Signal Passenger Side Grey w/ White Wire to Right Turn Signal Hopefully this helps! 451964

Thanks George, everything is working as expected.
Justin - 11/14/2018


- 119250KIT
2015 Mercedes-Benz GLA-Class

The directions for installation are poor at best. Quality looking harness. I will let you know if it works once I figure out how to install it. It is a universal harness, so it won't be too specific, but more description would have been better. 516051

The wiring harness you purchased for the 2015 Mercedes-Benz GLA-class does take a little bit of wire testing to determine how to install. First you want to use the wire tester that came with the kit to test the tail light wires on your vehicle. If you cannot locate the circuit tester from the kit I would recommend purchasing one such as part # 3808
Quickee Circuit Tester
. Using the tester, you will need to locate the functions of the wires. In order to determine which wire represents which function you will need to have a friend sit in the vehicle and perform each function while you are testing the wires. After you determine the functions you want to determine what style tail light you have by using the chart in the installation instructions. Follow the chart to attach your connectors from the kit to the corresponding wires depending on what type of wiring system you have, 2 wire system, 3 wire system, Brake tail multiplexed wiring or brake tail turn multiplexed wiring.
-- Heather A - 06/04/2018

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Ask the Experts about this Tekonsha Wiring

  • What Gauge Wire is Used for Tekonsha ZCI Trailer Wiring Harness to Connect to the Vehicle Battery?
    The ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit # 119250KIT uses 12 gauge wire to connect to your 12V battery. It is 20 feet long.
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  • Adding a 7-Way Trailer Connector on a 2013 BMW X5 to Power Trailer Brakes
    The easiest way to add a 7-way trailer connector to your 2013 BMW X5 is to start with a 4-way and then convert it to a 7-way. You can either hardwire in a kit, like part # 119190KIT, or use the ZCI kit, part # 119250KIT, instead. The ZCI sensors that clamp to your X5's wiring to detect the current flowing through the wires instead of being spliced in. This way you don't have to cut into the BMW's wiring. I've linked videos of both wiring harness being installed on X5's similar to...
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  • Recommended Trailer Wiring Harness for a 2016 Volkswagen Golf R
    I do have an option for you but the ZCI Circuit Protected Vehicle Wiring Harness part # 119250KIT is not recommended for use on your 2016 Volkswagen Golf R. Instead, you will want to use the Curt T-Connector Vehicle Wiring Harness part # C56374 which is actually a plug and play option that will not require you to cut or splice any wires like the original harness you inquired about does. With that being said, in order to hardwire a harness into your vehicle you would need to use a circuit...
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  • Recommended Equipment Needed to Tow with a 2015 Mercedes-Benz GLK350
    The Tekonsha ZCI # 119250KIT is confirmed to fit your 2015 Mercedes-Benz GLK350 and is a great option to use for a 4-Way flat connector. A more economical option (which fits the GLK250as you mentioned) would be the Tekonsha Upgraded Heavy Duty ModuLite # 119190KIT which is also confirmed to fit your GLK350 and will give you the same 4-Way flat connector. I like to recommend the Tekonsha electronic parts because they have received numerous positive reviews from customers and we have...
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  • How Does ZCI Trailer Wiring Kit #119250KIT Install on a 2015 Volkswagen Golf Sportwagen
    I checked with my contact at Tekonsha and he said to use the BTT code to install the ZCI part # 119250KIT that you have. This means to to run the yellow to the vehicle brake/tail/left turn, green to the brake/tail/right turn and then the brown and red wires would not be used. It sounds like you have tried using the B configuration and that is why you are having problems. I attached a diagram that shows the different ways you can use this box to wire up to a vehicle. To answer...
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  • Will a 2012 Mercedes-Benz ML350 Need to be Recalibrated After Installing Trailer Light Wiring
    You will want to install the Tekonsha ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector # 119250KIT for wiring on your 2012 Mercedes-Benz ML350. This product draws power from the 12V lead that is run to the battery and then sends a signal to the trailer connector once it detects that your light functions are being utilized. It does not require anything to be recalibrated on any vehicle that it is installed on. I confirmed this with my contact at Tekonsha....
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  • Trailer Wiring Harness Recommendation for 2019 Volkswagen Golf Alltrack
    The trailer wiring harness I recommend for your 2019 Volkswagen Golf Alltrack is the ZCI kit part # 119250KIT as it installs without requiring you to splice into the taillight circuits of the vehicles like the other options require. Instead of requiring splices it uses sensor that wrap around the wires to get the signal. If you are in need of a hitch the Draw Tite part # 24949 is a great option confirmed to fit as well! It's mostly hidden too so it's not as obvious when installed and...
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  • ZCI Circuit Protected Vehicle Wiring Harness 119250KIT Installation in 2017 BMW X5
    The ZCI Circuit Protected Vehicle Wiring Harness kit # 119250KIT includes a circuit tester like # 40376 to help you find the correct vehicle wires for harness installation. Since wire colors are not always consistent across production runs testing is the best way to ensure proper connection. This harness is universal so it will definitely work for you but the set-up steps outlined in the linked instructions need to be followed exactly. The linked installation video shows this kit in...
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  • Trailer Wiring Harness Recommendation for 2016 Audi Q5
    We have a trailer wiring harness for your 2016 Audi Q5 that does not require hardwiring to install. For that you'd want the ZCI kit part # 119250KIT. This kit uses sensors that attach to the wires instead of quick-splices so you have a very non-invasive wiring kit install. I attached an install video for this kit on a 2018 Audi Q5 which will be very similar to your 2016 Q5.
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  • Troubleshooting Curt Trailer Wiring of 2017 Honda Ridgeline Not Functioning After Install
    Did you use a circuit tester like part # PTW2993 to test all of the 4-way pins of the wiring harness part # C56365? I'd start there maybe but also make sure you installed all of the fuses and relays of this kit too.
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  • Troubleshooting Lights Staying On After Installing Tekonsha ZCI Vehicle Wiring Harness on RAV4
    The Tekonsha ZCI Vehicle Wiring Harness # 119250KIT that you installed on your 2019 Toyota RAV4 can be extremely sensitive with regards to the initial setup. Because it uses zero-contact sensors to identify current flowing through each wire, all the steps need to be followed exactly as written in the install manual. If the lights are staying on after initially activating them then this could be an indication that the magnetic sensors were simply installed in the wrong direction. Try...
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  • Does ZCI Wiring Harness Work on 2008 Land Rover Range Rover
    The ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit # 119250KIT is a universal fit that will absolutely work on your 2008 Range Rover and won't have any affect on your other wiring or interfere with it. This kit simply clamps onto the tail light harnesses in your vehicle and you will also need to run a hot lead to your battery to power the unit. I have added a link to a video install for you as an example so you can get an idea of the...
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  • Best Trailer Wiring Harness For A 2016 Mini Clubman
    I have the perfect trailer wiring harness for your 2016 Mini Clubman. I recommend using the ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit part # 119250KIT as this is a complete plug and play kit that comes with everything needed for installation, including a test light. You will also want a mounting bracket like the part # 18144 to secure the trailer connector to the hitch receiver. As this kit only includes a 4-flat trailer connector,...
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  • Does ZCI Trailer Wiring Harness Make Install of 4-Way Easier than Standard Universal Kit
    With the part # 119250KIT you have to pull out the wiring of the vehicle to access the wires that lead to the taillights, similar to what you saw in the video you mentioned. Where this kit makes thing is easier is that instead of having to use a quick-connect to splice in to the wire once you have found the one you need by testing, you instead attach one of the black sensors of the kit around the wire. Easiest way to see how this installs is to check out the install video I attached...
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  • How to Install the ZCI Wiring Harness on a 2019 Volkswagen Golf Alltrack with Multiplex Wiring
    In regards to installing the ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector part # 119250KIT on your 2019 Volkswagen Golf Alltrack, you may need to attach the wire connector with the brown sticker to the rear license plate illumination circuit and the wire connector with the red sticker to the center high stop light if the stop position and tail lights pins inside the trailer connector on the above harness do not work after installing the wire connector with...
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  • Trailer Wiring Harness Options for a 2017 Mercedes-Benz Metris
    The only trailer wiring harness we have for your 2017 Mercedes-Benz Metris that will not require you to cut or splice any of the factory wires is with the ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole part # 119250KIT. This harness uses sensors that clamp around the signal wires in your tail light housing. If you are looking for a more cost effective wiring harness, I recommend the Upgraded Heavy Duty ModuLite Circuit Protected Vehicle Wiring Harness part # 119190KIT though you...
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    For a trailer wiring harness confirmed to fit your 2017 Mini Clubman S that does not require any splicing you'd want the part # 119250KIT which is a confirmed fit and will work well. It's not a custom fit that matches the connectors of your vehicle, but since it uses sensors instead of splices it will install without any hardwiring. For a ball mount you then would want the part # C45521 and then for a ball part # 19256.
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    The three options for a 4-pole wiring harness kit for your 2014 BMW X5, all shown on the linked page, are powered converter types that use a direct connection to the battery to provide the actual power to operate the trailer lights. The signals from the car serve only to trigger the converter but they do not power the lights. This feature provides isolation and protection for the car's internal wiring/circuitry in the event of a short or other fault on the trailer. A new harness is much...
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  • Does Trailer Wiring for 2017 Mercedes GLE 350 use 2 or 3 Wire Wiring
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    For your 2015 Volkswagen Golf Sportwagen the only trailer wiring kit we offer that has been confirmed as a fit is the part # 119250KIT. This will require that you run a wire up to the batter of the vehicle as well. I attached an install video that shows how it would install in a similar vehicle.
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  • How to Install the ZCI Wiring Harness Part # 119250KIT on a 2-Wire System
    It sounds to me like you have a 2-wire system on your 2015 Mercedes-Benz GLK. For vehicles that use a 2-wire system, the turn & brake functions are combined on one wire and the tail light function is on a separate wire. The easiest way to test the rear taillight connectors for the proper turn/brake and running lights signals is to use a circuit tester like part # 40376. A voltage meter is not necessary to install the ZCI Circuit Protected Vehicle Wiring Harness part # 119250KIT. In order...
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    We have two options for your wiring harness for your 2015 VW Golf SportWagen TDi. The least invasive option is the Tekonsha ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit # 119250KIT. This harness offers zero contact interface sensors to capture the signal from your vehicle without splicing into the wiring at all. This harness is designed to work with a wide variety of vehicles. The second option is the Curt Powered Tail Light Converter...
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  • Troubleshooting Trailer Tail Lights That Stay On with Tekonsha ZCI Wiring Harness on 2016 Golf R
    We know from Tekonsha training on their universal-fit ZCI Circuit Protected Vehicle Wiring Harness # 119250KIT that this item is very sensitive to the initial setup process, which must be followed exactly for correct operation. My technical contact at Tekonsha advised that the magnetic sensors in this kit are directionally sensitive. If one of these were clamped on in reversed orientation it would not function correctly. He suggested that you pull the fuse to let the circuitry power...
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  • Troubleshooting Tail Lights with Tekonsha Kit # 119250KIT on a 2015 Volkswagen Golf SportWagen
    In the instructions for the ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit # 119250KIT under the INPUT SENSOR - DETERMINATION heading there is an asterisk after the BTT configuration explanation. If you look at the bottom of that box the asterisk says that you may need to route the tail wire to the rear license plate illumination circuit and/or brake to center high stop light (see attached picture). I recommend taking this step as it...
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    For your 2010 335d BMW the trailer wiring harness you would want is the ZCI part # 119250KIT. This harness basically can fit any vehicle and due to it's advanced design does not require any splicing into the delicate taillight wiring of your vehicle. I attached an install video for this harness that shows it installing on a similar BMW to give you an idea how it installs.
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  • Where is the Article for Running the Power Wire on a 2015 Mercedes-Benz GLK350
    Yes, the article on routing a power wire is linked to this page for you to reference. It is a generic article though so it doesn't go into details about how to do so specifically on a 2015 Mercedes-Benz GLK350. If you are installing the Tekonsha ZCI Wiring Harness # 119250KIT or the Universal Installation Kit # ETBC7 then you would not want to tap into the fuse block. The 12V power wire for the wiring harness is designed to pull directly from the battery so that your OEM wiring remains...
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  • Trailer Wiring Harness Recommendation for a 2010 BMW X5
    For trailer wiring on a vehicle that requires a universal type harness the ZCI part # 119250KIT would be the best kit available since there would be no hardwiring required. The sensors are pretty big, but you should have no problem getting them around the wires of your 2010 BMW X5. I attached an install video that shows a hardware kit being used to install on a similar X5 as yours that shows you how to find the wires and which to use. In the video around the 1:07 mark you can see...
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