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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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ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit Plug and Lead 119250KIT
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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. Lowest Prices for the best wiring from Tekonsha. ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit part number 119250KIT can be ordered online at etrailer.com or call 800-298-8924 for expert service.
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Tekonsha Wiring - 119250KIT

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

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.


  • Provides a 4-way flat trailer connector at the back of your vehicle 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 vehicle'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 vehicle'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: vehicles 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 vehicle 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 vehicle'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 vehicle'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 vehicle'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 vehicle 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 vehicle.

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 vehicle'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

This Product Fits The Following Vehicles

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 Tekonsha Custom Fit Vehicle Wiring - Trailer Hitch Wiring - 119250KIT Review

Today, we're going to be taking a look at the ZCI Circuit Protected Vehicle Wiring Harness with a 4-Pole Flat Trailer Connector. It's also going to come with the installation kit. This product is from Tekonsha. This unit's going to allow you to install a 4-way flat trailer connector on your vehicle without cutting or splicing into the vehicle wiring system. It's going to feature Zero Contact Interface sensors. That's going to be these components right connected to the end of the wires. These identify the current flowing through each wire simply by clamping onto the wire.

Again, no cutting or splicing in the wiring system is needed. The unit's going to provide your 4-way flat trailer connector at the back of your vehicle to power your trailer signal lights. This is compatible with 5-pull, 6-pull, and 7-pull adapters. Adapters are sold separately. It's going to come with a dust cap for the 4-way flat connector. That way, you can cover up the connection points when the plug's not being used.

You'll see here that we have plenty of wiring for the 4-way flat connector. I just have it all bundled up to keep it nice and tight for our video. Now, another main feature of this system is that it's designed to bypass the factory wiring. Again, no cutting, no splicing, and no plugging into the vehicle's wiring is needed. It's going to have these really unique sensors. These are going to clamp onto the wires of your factory tail light wiring harness, and that's going to be what detects the current.

The sensors are epoxy-filled to protect the sensors from the elements. No feedback, no interference with, and no power draw from your vehicle's wiring system. The unit's also going to include a circuit tester to insure proper set up. Again, once you have the wires ran through there . They got the little groove so they can sit in there nicely .. all you got to do is clamp that down until it snaps into place.

Then, it's going come with these foam pieces of tape. You wrap those around the center and that's going insure that they won't move around during operation. Simply wrap the foam tape around the sensor after the connections have been made. Now, this unit's also designed to automatically shut off if it detects a short or overload so it's completely designed for safety and to protect your system. Another neat feature about the unit is that it's easily removable and transferable between different vehicles. It's going the circuit protected module. That's going to connect directly to the vehicle battery for power. Comes with everything necessary to make that connection. This unit is designed to work with 2-wire, 3-wire pulse width modulation or PWM and multiplex wiring systems. It's going to work with standard incandescent tail light bulbs and LEDs. It's going to be constructed using surface mount technology for consistent reliable performance. What that does is it maximizes the trailer light yield and intensity while producing minimal heat and it insures superior operation even in rougher conditions. Now, this does feature a universal design and the system is designed to work on almost any vehicle. Just make sure that the vehicle operates on a 12 volt negative ground system, and you should be set to go. When it comes to the maximum amperage for the stop and turn light, it's capable up to 4.2 amps per circuit. For the tail lights, it's capable of up to 7.5 amps per circuit. When it comes to the installation, it's pretty simple. It's going to come with detailed installation instructions to walk you through that process step by step. Basically, what you need to do is you would need to connect these sensors onto the correct wires of your vehicle's wiring system. Each sensor's going to be labelled. This one says, "Left turn". This one says, "Right turn." They're color coded. This one says, "Stop," and this one says, "Tail." That shows you the functions of those sensors. You got plenty of wiring to work with. Again, I just have it all bundled up for video purposes, but you should not have any issue reaching the connection areas. Plenty of wiring is available with this system. Connect the sensors and again, they include the circuit tester right here so you can detect the correct wires that you're making the connections to. Once you get all those connected, you'll need to mount the box. You can do that using some double sided foam tape. You can do it using zip ties. It's also got a mount hole right here that you can use a screw to get it installed, but you want to get that mounted to a nice, clean, out-of-the location. Then, you'll also need to make a ground connection. That's going to be your white wire. Has a ring terminal already attached to it. The unit's going to come with a grounding screw so you can easily get that connected. Then, you'll need to run a hot lead to the vehicle battery. That's going to be the black wire coming out of the box. You would connect this to the bundle of black wire with one included butt connectors. The other end of the black wire gets connected to one half of the fuse holder with another butt connector. The other end of the fuse holder gets a ring terminal attached to it and gets connected to the positive post to the vehicle battery. It's got the fuse cap here. The 15 amp fuse goes directly in there. Close the cap. It's going to keep it safe and protected. Then, you would need to secure the excess or slack in the wiring with the included zip ties. It's going to come with a whole bunch of those to get your wires safely secure and up and out of the way. Once your installation is complete, the 4-way connector's going to be stowed in an out-of-the-way location, either within your cargo area or beneath the vehicle in the other trailer hitch. If you choose to mount the connector in the other hitch, we do recommend using a mounting bracket. Those are available here at etrailer.com with variety to choose from, and they are sold separately. It's also recommended that you use a small amount of dielectric grease in all your electrical connections like the 4-pull connector. That's really going to help prevent corrosion to those connection points. That's sold separately as well, and you can find it right here in etrailer.com. That's going to do for today's look at the ZCI Circuit Protected Vehicle Wiring Harness with a 4-Pole Flat Trailer Connector and installation kit.

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   (185 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

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 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
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
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
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

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
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
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

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

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

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

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

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
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
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
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
2018 BMW X5

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

- 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
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
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

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
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


- 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 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

Show More Reviews

Ask the Experts about this Tekonsha Wiring

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