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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 # 118721
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Custom Fit Vehicle Wiring

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Tekonsha Trailer Hitch Wiring - 118721
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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. Powered ModuLite reduces strain on wiring system. Call 800-298-8924 to order Tekonsha custom fit vehicle wiring part number 118721 or order online at etrailer.com. 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.
  • All Info
  • Reviews (5)
  • Q & A (6)
  • Videos (1)
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Tekonsha Custom Fit Vehicle Wiring - 118721

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

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. 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
    • Locate connection points in rear cargo area
    • Plug in T-connector
    • Run hot lead to car battery
  • Includes ModuLite power converter to ensure that your vehicle's wiring matches that of your trailer
    • Powered module connects 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:
    • Stop/turn lights: 4.2 amps per circuit
    • Tail lights: 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 inside your rear cargo area, on both the driver's side and passenger's side. You will have to remove the rear threshold and felt trunk liner to access this harness. Once you've plugged in the T-connector, run the hot lead up to your car battery. Connect the lead to the included fuse holder, and then connect the fuse holder to the positive terminal on your battery and insert the provided fuse.

Once installation is complete, the 4-way connector will be stowed in your rear cargo area.

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 your vehicle runs on a multiplex wiring system, the wiring needs to be converted to be 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.

118721 Tekonsha T-1 T-Connector - 4 Wire - Modu-Lite Converter Included

Installation Details 118721 Installation instructions

This Product Fits The Following Vehicles

California residents: click here

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

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 - 118721 Review

Today, we're going to be taking a look at a T-One vehicle wiring harness with a 4-pole flat trailer connector. This product fits certain years and models of the Volkswagen Passat. To see if this is a fit for your vehicle, you can use the vehicle fit guide located at etrailer.com. The unit's going to provide a 4-way flat connector at the back of your vehicle to power your trailer's signal lights. This is compatible with 5-pole, 6-pole and 7-pole adapters. Your adapters are sold separately.

It's also going to come with a dust cap for the 4-way flat connector. One of the things that makes this harness a little bit different than others is that the dust cap is actually tethered to the housing. That way it's always connected. You don't have to worry about misplacing that or losing that but that cap basically just goes over the connection points and keeps them protected when the plug's not being used. The black box on the unit, this is the included module light. This is a power converter that ensures that your vehicle's wiring matches that of your trailer's so the power module connects directly to the vehicle battery through the wiring which is going to avoid overloading the vehicle's electrical system. The unit is designed to connect quickly and easily.

All you have to do is locate the connection points in the rear cargo area and plug in your T connectors. These connectors are custom fit for your vehicle. They're going to match up perfectly with the ports on the vehicle and they're going to snap off together for a nice, tight, secure fit. The connector with the green wire goes to the passenger side of the vehicle. The connector with the yellow wiring goes to the driver's side of the vehicle. Once you get those connected, you'll need to make a ground connection.

That's going to be your white wire with the ring terminal already attached to it. You want to get that grounded to a nice, clean metal surface with the included grounding screw. Then, you'll need to mount the converter box to a nice, clean, out of the way location with the included double-sided adhesive foam tape. Once you have all that done, you're going to need to run the hot lead to the vehicle battery. The hot lead is the short, black wire that comes out of the converter box. This is going to get connected to the bundle of black wire with one of the included butt connectors.

The other end of the bundle runs to the vehicle battery and gets connected to one-half of the fuse holder with another butt connector. The other half of the fuse holder gets a ring terminal attached to it and gets connected to the positive post of the vehicle battery. It does come with your 15 amp fuse, goes directly in here. It's got the fuse cap that goes over it to keep it safe and protected. Once you have that done, you can go and secure any wires that you have with the included cable ties. What I mean by that is you want to secure any excess or slack in the wiring. You want to make sure your wires are up and out of the way and safely protected. We do recommend that once the installation's complete, that the the 4-way connector is stowed in your rear cargo area. There'a plenty of wiring so that way, you can pull it out of the back of the vehicle when you want to use it. When you don't want to use it or when it's not being used, you can bundle it back up and put it back in the rear cargo area. That way it's out of the way and it's protected from the elements. It's also recommended that you use a small amount of dielectric grease on all your electrical connections like the plugs on the vehicle and the 4-pole protector itself. That's going to protect the connection points from any type of corrosion. You can find that grease here at etrailer.com and is sold separately. When it comes to the maximum amperage for the stop and turns lights, we're looking at 4.2 amps per circuit. For the tail lights, we're looking at 7.5 amps per circuit. I also want to mention that this comes with detailed installation instructions to help walk you through the entire process step by step. That's going to do it for today's look at the T-One vehicle wiring harness with a 4-pole flat trailer connector.

Customer Reviews

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector - 118721

Average Customer Rating:  5.0 out of 5 stars   (5 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. Powered ModuLite reduces strain on wiring system.

- 118721

I had the local Haul dealership install this after purchasing. Everything works fine. The wiring is hidden in the trunk until you are towing and then you just hang it out of the trunk area while in use. Pretty clean install overall. As many have stated, running the power wire is the only hassle. My installer went under the car to the engine bay. 717507

- 118721
2016 Volkswagen Jetta

I just wish I had found trailer.com 24 hours sooner. I needed to put a trailer hitch and wiring harness on my 2016 vw Jetta..I searched online and found the hitch at our local branch of a major auto parts dealer. I went there to order the hitch and harness. The ordered the hitch but they didn’t have the harness. I came home and went back to the internet to search some more. I soon found etrailer.com where I ordered the harness. I continued to explore their site on when I saw that they had the exact hitch I had purchased and installed. Then I saw that I had paid a full $60 more for it. The wiring harness was plug and play at its finest. Everything fit and worked exactly as the directions explained it. I will recommend to others and this is my go to site for anything trailer. 695972

- 118721

Great product. Easy to hook up. Was sent the wrong part due to VW mid year model change. Customer service was excellent! Correct part in a couple of days. Working great! 566447

- 118721
2017 Volkswagen Passat

I installed this wiring harness on a 2017 Passat SE. Yes, an SE not an S model. etrailer customer support was fantastic in figuring out the problem. I originally purchased the 118742 kit and only the tail lights worked - no signal lights or brake lights. Customer service sent a new unit assuming the first was wrong. Still didn't work. I talked to Tommy in tech support and he called Tekonsha and found out there is a slight difference in how the SE and S models pickup power signals for lights. He also learned that VW sometimes interchanges wiring harnesses between models. He sent me the 118721 kit and the lights all worked. Keep in mind this kit is Not supposed to fit my car! The take away: etrailer could have said "your car is screwed up". Instead they worked to find a solution. They went above and beyond to make sure I could get my trailer light system to work. I have purchased several hitches, wiring harnesses and other items from eTrailer in the past. I was a loyal customer. Now I think I am a disciple! Thank you to Tommy and the philosophy of etrailer's customer service group. Does this product work? Yes. More importantly, etrailer's commitment to solving customer issues makes any purchase from them a safe bet. Thanks again Tommy! 508489

Wiring harness still working fine. The customer service story is still the best I have ever experienced. Thank you again.
James P - 05/14/2019


- 118721
2017 Volkswagen Passat

This is an excellent trailer wiring kit for my 2017 R-Line Passat. The instructions are straight forward and easy to follow with clear diagrams included. The wiring connectors lock into place making the installation quick and painless. Removing the trim to install the kit takes a bit but that's VW's fault. Running the black wire to the battery is easy once the car is up in the air. Nice kit! 334394


Ask the Experts about this Tekonsha Custom Fit Vehicle Wiring

  • Needing a Wiring Harness to Fit a 2017 Volkswagen Passat SE
    I have the answer for you. For your 2017 Volkswagen Passat the Tekonsha T-One Wiring Harness, # 118742, is the confirmed fit for your SE model. The connector will plug in to your Passat's factory wiring and will provide a 4-pole flat connector for your vehicle. The harness will include a ModuLite convertor that will ensure that your Passat wiring will match the trailer you will be wanting to tow.
    view full answer...
  • Wiring Harness Compatible with 2017 VW passat TR line [canadian trendline]
    I reached out to my contact at Tekonsha and the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118721 is a fit for your 2017 VW Passat TR line (Canadian trendline) vehicle.
    view full answer...
  • How to Determine Towing Capacity of 2018 VW Passat
    The best way to determine what your vehicle can tow is by looking at its owner's manual. Unfortunately, VW manuals are hard to find online unless you own the car already so I don't have a way to look at it for you. From the research I did it seems that the max towing capacity of your 2018 Passat is 1,000 pounds which sounds pretty likely. I recommend checking your manual to be certain though. Once you know how much you can tow you'll need the parts to do it. The hitch I recommend...
    view full answer...
  • Hitch Recommendation for 2019 VW Passat With Easiest Install Process
    If it were my Passat, I would go with the EcoHitch # 306-X7317 because of the options it gives for accessories. The install is more involved than others, but I think this is the best choice. You'll only install the hitch once, but you will use it for much longer and will find the extra effort is well worth it. There are 3 different hitches that are confirmed to fit your 2019 VW Passat Wolfsburg edition, Draw-Tite Sportframe Trailer Hitch # 24880, the Curt Trailer Hitch Receiver # C11234,...
    view full answer...
  • Correct Trailer Wiring Harness for a 2017 Volkswagen Passat SEL with LED Taillights
    The correct T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector for your 2017 Volkswagen Passat SEL with LED taillights is part # 118742, not part # 118721 which is for the S model.
    view full answer...
  • Recommended Hitch and Towing Accessories for 2019 Volkswagen Passat
    For what you're using the hitch for, you'd be fine with a low-cost option such as the Draw-Tite Class I receiver, part # 24880 but if you were planning on also using the hitch as a mounting location for a bike rack or a cargo carrying tray, you might be better off going with a 2 inch receiver like what would be provided by the EcoHitch # 306-X7317. There are many more accessory options that are compatible with a 2 inch receiver, so if you were going to use the hitch for something other...
    view full answer...

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Info for this part was:

Edited by:
Lindsey S
Installed by:
Cole B
Written by:
Alexander C
Updated by:
Isabelle B

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