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  1. Custom Fit Vehicle Wiring
  2. Tekonsha
  3. Custom Fit
  4. Trailer Hitch Wiring
  5. 4 Flat
  6. Powered Converter
T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

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

Item # 118713
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Custom Fit Vehicle Wiring

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Tekonsha 4 Flat Custom Fit Vehicle Wiring - 118713
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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. 1-800-496-5010 to order Tekonsha custom fit vehicle wiring part number 118713 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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  • Reviews (14)
  • Q & A (0)
  • Photos
  • Why etrailer?

Tekonsha Custom Fit Vehicle Wiring - 118713

  • 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. 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 behind tail lights
    • Plug in T-connector
    • Connect hot lead to car battery
  • 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:
    • 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 behind the driver's-side and passenger's-side tail lights. You will have to remove the tail light assemblies to access this harness.

T-One Connection Location Points Behind Tail Lights

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 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.

118713 Tekonsha T-1 T-Connector - 4 Wire - Modu-Lite Converter Included

Installation Details 118713 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 - 118713

Average Customer Rating:  4.4 out of 5 stars   (14 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.

2016 BMW 3 Series

This wiring harness was plug and play. I did not have to splice any wires, except for the positive and negative power which I connect both directly to my car battery. I also soldered and heat shrink the extension wire that goes to the battery so there is no bad grounding issue here.

It's unfortunate, but I think I got a faulty unit. The brakes work, the hazards work, but the tail light, right turn, and left turn functions do not work. Right turn signal blinks both trailer lights like hazards while the left turn signal does not turn on any lights.

I used a tester (vehicle lightbulb) on the 4 pin output of this harness and and found that:

GND (Black Wire) to tail light (Brown wire) does not turn on at all under any test case (tail light on, right turn, left turn, brakes, or hazards.

GND and Left turn (Yellow wire) produced output under hazards, brakes, and right turn, but does not blink under left turn case.

GND and right turn (Green wire) produced output under hazards, brake, right turn, but nothing on left turn.

I tested this on my trailer that also went to [retailer] and tested on their trailer as well and got the same result.

I went so far as to swap my right and left tail lamp connectors and got the same result, hazards, brakes, and one of the turn signal blink like hazards.

You mentioned the issues that you were having the wiring harness. Based on the issue with the right turn signal causing flashing with both sides, I recommend checking the ground on both the vehicle side and on the trailers side. I have an FAQ that can help with I have linked below.
-- Etrailer Expert Jenny N - 06/20/2022


I used this harness on my 2016 BMW 328 xDrive. Took my time, followed the instructions, and it worked well. The only mystery was finding access for the power wire to the trunk battery compartment, and I had to get creative. I ran the black power wire up through the right taillight area. Then I used the taillight location hole for access to the battery located below. I had to clip off the taillight location pin to keep from pinching the wire when reattaching the taillight but it fit and bolted into position with no problems.

2018 BMW 3 Series

Great design and good instructions for install. I was able to follow the instructions and get it installed by myself, but would recommend a second set of hands for removing and installing the bumper skirt as instructions suggested, just to avoid damage.

2017 BMW 3 Series

Perfect fit, lights work on trailer and didn't mess up the lights on the car. The plug-n-play was great!


Instructions made for a productive installation. Harness is still working well after a year.


The trailer hitch, the mechanical part, was straight forward. The YouTube assist was good. My problem was the electrical harness with the plug and play concept. It was easy to install, but once, installed didn't work. I contacted your company and got some assistance. The solution was to cut the four wires and splice them back together after some trial and error to find out what worked. I have a 2015 and a 2016 BMW. The 2015 had to be modified, but the 2016 seemed to be fine. I noticed that BMW had re-oriented their color code for some reason. Both cars look and handle the same, but they changed the functional sequence of the four wire cluster.


its almost a plug and play kit you still need to wire the box to your battery luck for me on the bmw 3's the battery is in the trunk so you only need to run it a few feet. Seems to be good quality and works well the only complaint I have is that when you go to re install the taillights the wiring gets in the way, however with a few well placed zip ties it all fits together.

2016 BMW 3 Series

The hitch fits absolutely perfect on my car.
The wiring harness is barely long enough, and the connectors for the taillights should have more to be able to bury the connectors someplace. There is very little room behind the taillights for the extra connectors. Was difficult to get the driver side to fit, but eventually it worked. 3 more inches of wire on either side would have helped a great deal.
I will still recommend this product, as it is a very neat and clean install.

2016 BMW 3 Series

Was pretty easy but I am a mechanic so... just followed the video went smooth. It's a one man job, installing hitch. The only thing is the wire ties don't fit around the hitch, but I had some larger ones on hand. So easy breezy beautiful!


well-made, fits well, good quality, good corrosion protection, relatively easy installation.


Easy Peasy
No Problems


Great product! Works great, no error message on dashboard!! Installed on my BMW 3series with no issues at all!!


Easy to install and works great!



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

  • Hitch and Wiring for a 2016 BMW 328i
    I contacted Horizon Global and they advised me that removing the heat shield as apposed to trimming when installing the Draw-Tite Sport frame Trailer Hitch Receiver - Custom Fit - Class I - 1-1/4" Item # 24945 on your 2016 BMW 328i is acceptable. I also recommend the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector Item # 118713. It connects directly to factory plug behind each taillight. The wiring harness has a converter box that will protect back feed from the trailer...
    view full answer...
  • Trailer Hitch Receiver Fit for 2016 BMW 328i xDrive Wagon
    I checked with the manufacturer for you, and verified we do have a fit for your 2016 BMW 328i xDrive Wagon, which is the following: - Curt Trailer Hitch Receiver # C11367 This is a bolt-on trailer hitch that won't require any drilling into your BMW's frame and will fit your 328i xDrive perfectly. Additionally, if you were going to do some light towing and also needed a trailer wiring harness, the correct part for your BMW is the T-One Vehicle Wiring Harness # 118713. I have added links...
    view full answer...
  • Trailer Hitch Recommendation for 2017 BMW 320i Sedan
    For a hitch for your 2017 BMW 320i the Draw Tite hitch part # 24945 is what I recommend because it would do a great job towing a small trailer as it has a 2,000 lb trailer weight capacity and also has a concealed crosstube which makes it less visible than other options. For trailer wiring the T-One kit part # 118713 is what I recommend because it has our most reliable converter box and is custom fit for your vehicle. For a hitch ball you'd want the part # 3593 which is what Draw Tite...
    view full answer...
  • Recommended Hitch and Wiring for 2016 BMW 328ix Gran Tourismo
    The best source for information on whether or not your 2016 BMW 328ix Gran Tourismo can tow this trailer is going to be the owner's manual; the Curt # C11367 has a capacity of 2000-lbs towing/ 200-lbs tongue weight, so it will handle a load that size but I am not able to find conclusive information on the vehicle's towing capacity with any of my sources. Additionally, removing or trimming the heat shield does not affect performance of the vehicle, so there's nothing to worry about in that...
    view full answer...
  • Trailer Hitch and Wiring Recommendation for 2017 BWM 330i XDrive Wagon
    The Draw Tite hitch you mentioned # 24945 actually does not fit the wagon models so it would not be the way to go for your 2017 BMW 330i Xdrive Wagon. What you would want is the Curt # C11367 instead which is a fit, is mostly hidden, and at a better price point than the totally hidden Stealth # SH33VR. I confirmed with Tekonsha too that the custom install trailer wiring harness # 118713 does fit your 2017 BMW 330i Wagon as well.
    view full answer...
  • Trailer Hitch and Wiring for a 2014 BMW 328 Wagon
    I'm guessing you meant you have a 2014 BMW 328 Wagon (as opposed to 238 Wagon). With that being said, pricing is fluid so it is very possible that you saw different pricing on the Draw-Tite # 24945 one day and then it was different the next. When it comes to wiring you can either use the ZCI # 119250KIT that you referenced, or the Universal Kit # 119190KIT if you're wanting something a little more cost effective. The universal wiring means you do need to splice into your OEM wiring which...
    view full answer...
  • Fit of Curt Class I Hitch C11367 on 2018 BMW 340i xDrive GT
    According to Curt, their # C11367 Class I hitch is a fit for all models of the 2018 BMW 340i xDrive including the GT model. If you'll be doing some light duty towing, you'll also need a trailer wiring harness like # 118713, a ball mount like # C45521, a hitch pin like # PC2 and a trailer ball like # A-80 for a 1-7/8 or # A-82 for a 2 inch ball. I've linked to an install video for the hitch.
    view full answer...

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Info for this part was:

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

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