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T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

Item # 118378
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Tekonsha Powered Converter Custom Fit Vehicle Wiring - 118378
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Quickly and easily install a 4-way trailer connector on your vehicle with this custom wiring harness. T-One connector plugs directly into existing wiring - no cutting, splicing or tapping required. Powered ModuLite reduces strain on wiring system. 1-800-496-5010 to order Tekonsha custom fit vehicle wiring part number 118378 or order online at Free expert support on all Tekonsha products. Guaranteed Lowest Price and Fastest Shipping for T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector. Custom Fit Vehicle Wiring reviews from real customers.
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Tekonsha Custom Fit Vehicle Wiring - 118378

  • Custom Fit
  • Trailer Hitch Wiring
  • 4 Flat
  • Powered Converter
  • Tekonsha

Quickly and easily install a 4-way trailer connector on your vehicle with this custom wiring harness. T-One connector plugs directly into existing wiring - no cutting, splicing or tapping required. Powered ModuLite reduces strain on wiring system.


  • 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)
  • Connects quickly and easily - no cutting or splicing of wires
    • Locate connection point along frame rail
    • Plug in connector
    • Plug in fuse holder under hood
  • Includes ModuLite to ensure that your vehicle's wiring matches that of your trailer
    • Powered module connects directly to battery to avoid overloading vehicle's electrical system
  • Constructed of 16-gauge bonded wire
  • Comes with dust cap for 4-way flat connector


  • Maximum amperage: 7.5 amps per circuit
  • 1-Year limited warranty


This custom-fit T-One connector plugs into your vehicle's wiring harness, which is located at the rear, along the driver's-side frame rail. Once you've plugged in the tow harness connector, locate the gray connector between the truck's battery and the fender at the front of your vehicle. Plug in the fuse holder wiring harness. Then attach the ring terminal at the opposite end of the harness to the positive terminal on your truck's battery. Insert the included 10-amp fuse into the in-line fuse holder.

Once installation is complete, the 4-way flat connector will be stowed beneath your vehicle, near the trailer hitch. A mounting bracket (sold separately) is recommended to keep the connector secure.

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

ModuLite Powered Tail Light Converter

A ModuLite power module is built into this T-One connector. Because most trailers run on a two-wire system - wherein the brake and turn signals are carried on one wire - the separate brake and turn signals from your vehicle's three-wire system need to be combined so they are compatible with the wiring system of your trailer. This power module functions as a tail light converter to combine the brake and turn signal functions of your automobile so that they run on one wire to properly activate your trailer's tail lights. Note: This will not affect how the tail lights on your vehicle operate.

With a ModuLite, your trailer's lights will be powered without overloading your vehicle's electrical system. Because the module draws power directly from your car's battery and bypasses the electrical routes that are used by a basic wiring harness, there is virtually no draw on your tail light circuits.

118378 Tow Ready T-1 T-Connector - 4 Wire - Modu-Lite

Installation Details 118378 Installation instructions

This Product Fits The Following Vehicles

California residents: click here

Customer Reviews

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector - 118378

Average Customer Rating:  4.8 out of 5 stars   (91 Customer Reviews)

Quickly and easily install a 4-way trailer connector on your vehicle with this custom wiring harness. T-One connector plugs directly into existing wiring - no cutting, splicing or tapping required. Powered ModuLite reduces strain on wiring system.

2002 Toyota Tundra

Perfect fit for my 2002 Tundra. Easy to install. Good instructions and video provided. Works great! etrailer has always been great for me!


I never got my wiring harnesses something must’ve happened when you guys sent it.

I will have our customer service team reach out to you.
-- Etrailer Expert Jenny N - 12/01/2021


Perfect fit and easy per fectly

2002 Toyota Tundra

etrailer made the process quite simple. Online videos, written instructions, 2 day delivery all contributed to a painless process. '02 Tundra with 320k miles. Everything fit perfect.


I had to return the first harness, it was my mistake. The person on the phone was very understanding and found the exact trailer wiring harness I needed, it was an older vehicle, hooked up perfectly!!

2002 Toyota Tundra

This is the easiest trailer wiring kit that I've ever used. There was no drilling for a ground screw, no running a power wire the length of the vehicle, no disassembling the taillights. The Tundra already had the modular connectors, all we had to do was tap into them. The hardest part was deciding where to put the zip-ties. This is a great product and I highly recommend it.

Still perfect - one year later!
TVillainX - 05/12/2020

2002 Toyota Tundra

This is excellent

2001 Toyota Tundra

The harness I ordered was installed on mu 2001 Tundra in ten minutes. Easy, excellent delivery time and completely satisfied. The boat goes to the lake tomorrow with every light on the trailer working. The videos were an excellent source for me. Reading instructions is not my strong suit.

This product is working just fine. Makes me feel like a competent install mechanic.
Michael K - 06/29/2016

Toyota Tundra

I've had a Hidden Hitch and wiring harness on my Toyota Tundra for a number of years. When I needed to get a 7 way plug I found that the old wiring didn't work. So I repmaced it and added a plug. The installation was easy and it works great. I wish there had been a single harness but replacing the old one and adding the 7 pin was very simple. I got great service from E-trailer and the video's were a good help. I'll use them again!

2002 Toyota Tundra

Was exactly as described. It took me less than 10 minutes to get the whole setup installed and tied up. The communication and shipping from ETrailer has be way above top notch. Highly recommend this company

Haven’t had any issues. Still works same as Day I installed it
Toby J - 10/15/2017

2001 Toyota Tundra

The T one wiring harness for my 01 tundra worked perfectly , I watched the installation video on the website and when it arrived it took less than ten minutes to install . E - trailer's description and customer service were excellent I highly recommend them and their products.


My 2002 Toyota Tundra was not powering my boat trailer properly. After a bunch of testing the Tundra wiring I isolated the problem to the Toyota converter/power module. I found a replacement wiring harness at etrailer that matched my vehicle. I have received the new wiring harness and reviewed the installation instructions. Everything seemed to match up to my existing Toyota wiring harness which gives me a lot of confidence the installation will be a no-brainer. If I do have questions or problems I am confident the etrailer staff will be responsive and able to help me out. Although I do not expect that that will necessary. etrailer kept me informed throughout my purchase transaction from confirmation of my order through delivery. I will definitely use etrailer again.

2002 Toyota Tundra

Needed this harness for my 2002 Tundra. The Tundra owners manual leads you to believe that the factory harness is ready to haul a trailer, but this is not accurate. I installed the T-One Vehicle Wiring Harness with 4 Pole Trailer Connector with no difficulty in about an hour (and that was taking my time!). Instructions were clear and had good photos. Product arrived faster than I expected, and customer support was quick to answer a question about which rear truck connector to use (it is NOT the connector just behind the license plate, but in my case over on the far left side behind the tail light). I will definitely shop at Etrailer again.


The product is exactly as advertised and arrived on time. Installed it and looks great.

Let me just start by saying that the product itself is not the most important thing. How many companies or sellers out there are reaching out to you and make sure that their product arrived on time and it met your expectations? And if not, following up and making sure they change that!? I am a big fan of etrailer and you have a great model going, keep up the good work and creativity to always stay a step ahead of the competitors.

BUYERS - Buy with confidence! You have nothing to lose when you are dealing with a seller that stands behind their product and customer satisfaction is their first priority!

Shoutout to Tommy C!


What can I say? This was the easiest install I've ever done. It literally took me 25 minutes to remove the old harness, then install and test this wiring harness and this is the first time I've installed anything like this. Etrailer responded to my online order within minutes and I had the kit delivered in 2 days. Great service, great product.......I'll be back in the future! Thank you etrailer.

2002 Toyota Tundra

The trailer wire harness and mounting bracket for my 2002 toyota tundra came in on time and was easy to install. It took about 20 minutes from start to finish. I appreciate everything and will shop with etrailer in the future.

2001 Toyota Tundra

The harnesses plugged right up and worked perfectly.
Great product!
Communication from eTrailer was the best. Package tracking was weak and did not provide enough info.
The eTraller website is easy to use & provides great info & instructions on the produce installation. Because the instructions were so good the purchase decision was no-brainer.
I definitely make eTrailer my first look for this kind of product.

2002 Toyota Tundra

Installed this on 2002 Tundra. Easy install and works fine one year later.


I received the wiring harness right away but haven't installed yet I hope soon but thanks

2002 Toyota Tundra

Very easy to install, perfect fit with the truck's existing connectors, good quality, and most important, worked flawlessly. I do recommend this product from


Instructions easy to follow. Received exactly what I wanted and worked as advertised. Took about 15min to install. Would recommend to anyone needing a trailer light harness.


The converter and the harness arrived in an easy-to-open packaging and with ample instructions. The device installed easily and worked as it was supposed to.

2001 Toyota Tundra

This was the easiest install for wiring ever. The product was perfect for matching up to my 2001 Toyota Tundra. Unplug and replug. Done. Afterwards, I tested it and everything worked perfectly.


This was an outstanding "plug and play" purchase. Etrailer continues to impress me with their DIY videos and ease of installation. This was a piece of cake to install. Continue the great work etrailer!!!

2002 Toyota Tundra

Works, Double sided tape came off - Used this one to replace same unit I bought 2 years before that died. If this one lasts only two years I will have one wired in.

Was very simple to wire in.

Show More Reviews

See what our Experts say about this Tekonsha Custom Fit Vehicle Wiring

  • Trailer Wiring Solution for 2002 Toyota Tundra
    It's hard to say but there is a pretty good chance a 2001 Toyota Tundra with a factory hitch came with trailer wiring. If you needed wiring though the part # 118378 is a custom fit option that would work well. This will give you a 4-way wiring harness.
    view full answer...
  • Wiring Up Third Brake Light for Truck Bed Camper Shell
    Sounds like you are trying to wire up the third brake light of a camper shell. The tow package wiring will not work because the turn signals and brake light circuits are on the same wire. You could use the third brake light at the top of the cap (if equipped) and tap into the brake light there by removing the light to access its wiring. Or you could use a fuse tap and tap the stoplights and high mounted stoplight Fuse - Position 29 - 15amp located in instrument panel fuse block. And...
    view full answer...
  • Does the Tow Ready Harness # 118378 Ground Separately or Through the Converter Box Harness
    There isn't a dedicated ground wire that needs to be ran to install the # 118378 harness you referenced. It grounds through the connection that the harness with the converter box is attached to. You only need to make that connection and then connect the other included harness to the positive post on your battery and it will be fully functional. I attached installation instructions and an install video for more info.
    view full answer...
  • How Long Would it Take to Install a Tow Ready Wiring # 118378 on a 2002 Toyota Tundra SR5
    This T-One Vehicle Wiring Harness with 4 Pole Trailer Connector, part # 118378, installs very easily. After looking at the instructions it looks like it should only take about twenty minutes or so to install this product on your 2002 Toyota Tundra SR5 Access Cab with a Lift Gate. Aside from needing access to basic tools, this product comes with everything you would need to install the # 118378. I attached installation instructions below for you to check out also. These should give a pretty...
    view full answer...
  • Trailer Wiring Harness for a 2002 Toyota Tundra
    I went out to the warehouse and pulled the trailer wiring harness, # 118378 to take a look at the plugs. There are actually 2 plugs, one that connects to a power receptacle on the truck for power and another one that plugs into the back where your receptacle is located. The harness does have 3 rows of plugs but the center row does have one pin right in the middle of the plug. This harness is the correct one listed for a 2002 Toyota Tundra. Take a look at the instructions for the harness...
    view full answer...
  • Fuse Location for 118378 Tow Ready T-One Vehicle Wiring Harness
    The 10 amp fuse for the # 118378 wiring harness is installed in the small yellow fuse holder, located on the smaller portion of the wiring harness that does not have the black converter box. This part of the harness would be connected underneath the hood of your 2002 Toyota Tundra. You would disconnect your negative battery cable, remove the battery hold down bracket, and slide the battery forward to locate the mating connector on your vehicle between the battery and fender. Remove the...
    view full answer...
  • Will Tow Ready T-One Wiring Harness # 118378 Plug Into The Factory Plug On A 2002 Toyota Tundra
    The T-connector plug on the Tow Ready T-One Vehicle Wiring Harness # 118378 will plug into the 11-pin factory plug located under the 2002 Toyota Tundra in the rear, close to the driver side frame rail. There is another connection that has to be made under the hood of your vehicle. You will need to move the battery and find a gray connector located between the battery and the fender. You will remove the plug in the gray connector and plug-in the trailer harness fuse holder connector that...
    view full answer...
  • Recommended Wiring Harness for 2001 Toyota Tundra
    For your 2001 Toyota Tundra, I recommend the T-One Vehicle Wiring Harness # 118378. This T-One connector will plug directly into the port located under the vehicle, which is referenced in the picture that you sent. This will provide a 4-Way connector to hook up with your trailer and activate its rear signal lights. I have also attached an installation video on your 2001 Toyota Tundra that you can use for reference.
    view full answer...
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  • Wiring Harness with OEM Connectors for 2002 Toyota Tundra
    Thank you for the photo of your 2002 Tundra's wiring connector. We do not offer any auto maker's OEM-style connectors by themselves, only as part of wiring harness products like T-One Vehicle Wiring Harness # 118378. The photo I linked shows the OEM-style connector on this item. You may need to go to a Toyota dealership or auto parts stores for just the connectors.
    view full answer...
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  • Trailer Light Not Working and Wiring Harness Show No Power on 2002 Toyota Tundra
    First, what I recommend is checking the converter box in the trailer wiring, # 118378, to determine if it is the harness or the truck that is the problem. Use a circuit tester like # 40376 if needed to test the wires going into the converter box from the truck. If the signals are correct going into the box, you know that the truck is not the problem. Then test the wires coming out of the converter. If the signals are all correct coming out of the converter, the problem is somewhere on...
    view full answer...
  • Would the Hidden Hitch part # 13184 Fit a 2001 Toyota Tundra Regular Cab
    Yes, the Hidden Hitch part # 13184 will fit your 2001 Toyota Tundra regular cab as it has been confirmed as a fit for all models of the 2001 Tundra. I attached an install video for you to check out as well. If you wanted to do some towing you might be interested in etrailer ball mount kit # 989900. It comes with 2 ball mounts; one with a 3/4 inch rise or 2 inch drop and one with a 2-3/4 inch rise or 4 inch drop. It also includes a 1-7/8 inch ball, 2 inch ball, hitch pin with clip, and...
    view full answer...
  • Is the Curt Converter Box for a 2002 Toyota Tundra Replaceable
    The converter box for the Curt T-Connector Vehicle Wiring Harness part # C55378 is not available as a separate replacement part unfortunately. However, I actually recommend you take a look at the T-One Vehicle Wiring Harness part # 118378 instead which we have found to be much more reliable. The issue that causes the converter boxes to fail is excessive movement. The above Curt converter box attaches using adhesive which is not always the best method. The Tekonsha converter box attaches...
    view full answer...
  • Low Voltage on Factory 4-Way Trailer Connector on a 2002 Toyota Tundra
    If the factory tow package wiring on your 2002 Toyota Tundra uses both fuses and relays then the issue could be a faulty relay. They can sometimes still allow some power to trickle back even if they are bad so that is one thing to check. There could also be a corrosion issue, ground problem, or wiring problem. If you are testing the pins on the 4-Way go ahead and test one of the wires going to the connector instead. If you get the proper voltage on the wire but not the pin then it is...
    view full answer...
  • 2002 Toyota Tundra Does Not Have Correct Plug to Match Recommended Custom Wiring, What Can I Use?
    It looks like the 2002 Toyota Tundra should have an 8-pin square connector on the rear of the vehicle for the trailer wiring, and from the photo you're showing that is definitely not an 8-pin square connector; it's a 6 pin square. One of two things could have happened here. I would first make sure that you've pulled the correct plug, since there are two very similar plugs placed right next to eachother on the 2002 Toyota Tundra. I've taken a screenshot of our installation video as a reference...
    view full answer...
    Image 1 for Image 2 for
  • Low Voltage From Converter 4-Way With Curt Harness on 2001 Toyota Tundra
    If you checked the wires right before the converter box of the Curt T-Connector Vehicle Wiring Harness # C55378 for your 2001 Toyota Tundra and got 12 volts, but then tested the wires coming out of the converter and got almost nothing, the issue will be a bad converter, which is rare but happens on occasion. I also do highly recommend going with a Tekonsha wiring harness for your 2001 Tundra, as they make the most reliable harnesses. The correct part for a 2001 Tundra is the Tekonsha T-One...
    view full answer...
  • Why Are My Trailer Taillights Staying On when Using the Curt Harness # C55378?
    If you have tested the Curt Harness # C55378 with a circuit tester on your 2001 Toyota Tundra, there should not be any signal to the plug when the vehicle has the lights off and there should be power to the lights when the vehicle is turned on. If you tested and there is a signal with the lights off, there is a problem with the vehicle's-side of the connection. To rule out any issues with the vehicle's-side of the wiring, make sure that there are no frayed/pinched wiring and that the ground...
    view full answer...
  • Troubleshooting Brake and Turn Signals Not Working on Trailer
    I'm not sure which wiring harness you replaced but we can cover the trailer and the vehicle side for troubleshooting. The first thing I would check is your 4-way connection. Make sure both connectors are clean and free from debris, and make sure they are not damaged. Once this is done, I would go ahead and check out the connection on the vehicle side using a circuit tester like the # PTW2993. You want to test to see if the brake and turn functions are working properly on the vehicle connector....
    view full answer...
  • Does a Wiring Harness Come with a Trailer Hitch for a 2002 Toyota Tundra
    Trailer hitches including # 75105 do not come with wiring harnesses. The reason is that some people aren't using the hitch for towing while others could be replacing a hitch and already have wiring. For your 2002 Toyota Tundra you can use # 118378 to add a 4-Way connector. If you need to add a 7-Way you would also need # ETBC7 in addition to the 4-Way. I have included some links that show and explain the ETBC7 installation for you.
    view full answer...
  • Transferring Prodigy P2 # 90885 Brake Controller from Ford Explorer to Toyota Tundra
    Since trailer brake controllers are not vehicle-specific you can indeed transfer your Tekonsha Prodigy P2 # 90885 from your Ford Explorer to your 2001 Toyota Tundra. You will need the trailer brake install kit # ETBC7 that you referenced. If your Tundra does not already have a working 4-pole flat trailer connector at the rear bumper you will first need to install one. There are both hard-wire types (cutting and splicing required) and custom-fit plug-in types, which is what I suggest. You...
    view full answer...
  • Parts Needed to Install a 7-Way Trailer Connector on a 2001 Toyota Tundra With Existing 4-Way
    Your best option is to install our Universal 7-Way and 4-Way Installation Kit, part # ETBC7. There are no plug-in style 7-way trailer connectors that will replace the Tow Ready harness on your truck, but the ETBC7 will use your existing 4-way and provide the additional hardware and wiring needed to have a fully functioning 7-way trailer connector. I attached an installation video on a 2002 Toyota Tundra to give you an idea of what will be involved with the installation. The installation...
    view full answer...
  • Truck/Trailer Brake Lights Come on with Trailer Connected and not Using Brakes, 2001 Toyota Tundra
    From what I have been able to gather, the 2001 Toyota Tundra did not come with a tow package that included trailer wiring connections. This could mean that it was done aftermarket and could have been wired incorrectly by a previous owner. Or there could be a bad ground issue causing the malfunction. I recommend checking the ground connections on the truck and trailer side connectors. They will need to be clean and free of corrosion. I spoke with one of our installers about this problem....
    view full answer...
  • Availability of Brake Controller Harness for 2001 Toyota Tundra
    If you are looking for a brake controller harness, there are none available for the 2001 Toyota Tundra. The 2001 Tundra did not have factory tow packages as an option, so a brake controller will have to be hard wired into the vehicle. You will need part # ETBC7 to create a 7 way plug at the rear of the truck. I will include a video on this kit. You will also need to install a 4 way connector. Toyota put the provision in for this so you will need part # 118378. Once you have these parts...
    view full answer...
  • Parts Needed to Install Prodigy P2 Trailer Brake Controller 90885 in 2001 Toyota Tundra
    It sounds like you want to install an electronic trailer brake controller in your 2001 Toyota Tundra. We can help you with the items you need. For a brake controller I recommend the popular and easy-to-use Prodigy P2 # 90885. This controller offers the best mix of features and proven reliability. If the Tundra does not have any trailer wiring you will also need to add a 4-pole harness such as # 118378. Then all you need is our brake controller install kit # ETBC7. This includes the 7-way...
    view full answer...
  • Troubleshooting Installation of Curt 4-Pole Wiring Harness C55378 in 2002 Toyota Tundra
    The two wiring harness kits you referenced, Curt # C55378 and Tekonsha # 118378, are both correct fits for your 2002 Toyota Tundra. Both of these kits are multi-part harnesses that include the required fuse/fuse holder and the installation of the Curt kit in a 2002 Tundra is shown in the linked video. The troubleshooting steps I suggest are to double-check that all connectors have no bent or damaged contacts, that they are fully seated together and that the ring terminal on the harness...
    view full answer...
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