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

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

Item # 118725

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Custom Fit Vehicle Wiring

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Tekonsha Trailer Hitch Wiring - 118725
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In Use/Installed

  • 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. Call 800-298-8924 to order Tekonsha custom fit vehicle wiring part number 118725 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 (10)
  • Q & A (1)
  • Videos (2)
  • Photos
  • Why etrailer?

Tekonsha Custom Fit Vehicle Wiring - 118725

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 - no cutting or splicing of wires
    • Locate connection point behind rear bumper
    • Plug in T-connector
  • Includes relays required to activate functions
  • Constructed of 16-gauge bonded wire
  • Comes with dust cap for 4-way flat connector


  • Maximum amperage:
    • Stop/turn lights: 7.5 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 your rear bumper on the driver's side. Once you've plugged in the T-connector, locate the relay box in your rear cargo area and insert the included relays as shown in the instruction manual.

Once installation is complete, the 4-way 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.

118725 Tekonsha T-1 T-Connector - 4 Wire

118725 Installation InstructionsInstallation Details 118725 Installation instructions

This Product Fits The Following Vehicles

2016 - 2019 Buick Envision

2016 - 2019 Buick Envision with factory trailer connector

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 Vehicle Wiring Harness Installation - 2017 Buick Envision

Speaker 1: Today on this 2017 Buick Envision, we'll be having a look at and showing you how to install the Tekonsha T-One Vehicle Wiring Harness with a Four-Pole Flat Trailer Connector, part number 118725.Here's what the wiring harness looks like installed. This wiring harness will allow us to safely and legally tow a trailer with the lighting functions that are required by law. Our white wire provides the necessary ground connection between our Envision and our trailer. Our brown wire is for our tail light and running light circuit. Our yellow wire is for our left brake light and left turn signal, and our green wire is for our right brake light and right turn signal.Now, on these three wires we have a total power output of 7.7 amps of power per wire. That's going to allow us to tow a trailer that has several incandescent lights on it.

If we're using LED lights on our trailer, they draw significantly less power than incandescent lights, so we shouldn't have a worry. We can be able to run about as many as we want.Now, this wiring harness also has a dust cover built in that's permanently attached to the four-pole connector, and this will help protect it from the elements when it's not in use. What I like to do is to put some dialectric grease inside the connector. Then, you can connect it around your safety chain leads on your hitch to help store it up and out of the way, and it won't dangle underneath your vehicle when you're not towing your trailer. It'll be readily accessible when you're ready to use it.

This wiring harness is a quick and easy install. It goes right into your factory tow package on your vehicle. Now that we've gone over some features, we'll show you how to get it installed.The first thing we need to do is locate our vehicle's factory tow harness connector. We will locate that on the driver side of our frame rail towards the rear just above our tailpipe. It's this connector right here.

So, we can grab this. With it pulled down, it's more accessible for us now. We have this red tab we'll slide back. That unlocks it. We can press on this black tab and pull to separate the plug.Now, we'll take our wiring harness and we'll plug it into the factory tow package connector.

With it clicked in place, we'll pull back make sure it's secure, and we'll resecure it to the side of the vehicle. We went ahead and routed our wiring harness over towards the center of our vehicle going behind our fascia over our hitch tucking up the excess and e secured it to our safety chain loops with the provided dust cover.Now, we'll open our rear hatch. We'll open the panel on the driver side, and inside we'll find two unoccupied spots for relays. We'll take our provider relays. These can only go in one way, so we'll line them up appropriately. Both of these are the same. We'll push them in the slots. We'll replace the cover now.Okay. Now, we'll test our wiring. We're using a four-pole flat tester. It's part number I26 on our website. The reason we're using this over just hooking up to our trailer is if we have a problem with the trailer we wouldn't be able to tell if the vehicle's working properly. Turn our headlights on. Our tail light and running light functions' working properly. Left turn signal now, that's working. Right turn signal, that's working as well. Step on our brakes, those are working, and we'll test our turn signals while our foot's on the brake to make sure everything's working properly. Perfect. Everything's working as intended.That completes our look at and showing you to install the Tekonsha T-One Vehicle Wiring Harness with a Four-Pole Flat Trailer Connector, part number 118725, on this 2017 Buick Envision.

Customer Reviews

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector - 118725

Average Customer Rating:  5.0 out of 5 stars   (10 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.

- 118725

Easy install and works perfectly.... only complaint is that the directional is louder than normal. Other than that we are very pleased and would buy from you again. Thanks! 614237

- 118725
2016 Buick Envision

Product arrived and packaged perfectly, no damage. Also received the other items and everything was exactly what I need. If the weather holds I hope to install the new hitch and wiring this weekend. If not, oh well. Looks like the install is going to be quick and easy just the same. Thanks for the great service. 339895

- 118725

Everything worked as it should. Wire harness was simple to install. Hitch went on easy as well. 716754

- 118725

As advertised. Fits, works and easy to install on the 2019 Buick Envision. Fair price. 695191

- 118725
2017 Buick Envision

Quality products, very easily installed. I ordered the wrong wiring harness, When I realized it, I immediately contacted by e mail, they responded quickly and told me to reorder the correct one, and steered me to the site for a prepaid return label. The wrong one came with the hitch, Two days later,the correct one came. I installed the hitch the day it arrived, I installed the harness today and sent the wrong one back. ( boxed it up and applied the label I printed off the website) Took it to the UPS store, no problems. I'll probably order one for my older car also 692717

- 118725

Easy to install and works great 667948

- 118725

plug and play worked great with new hit ch 352629

- 118725
2017 Buick Envision

The wiring kit (item: 118725) had all parts required and fit my Buick Envision perfectly. The instructions were clearly written and also had pretty good pictures showing where to install the relays in the fuse box. Thanks! 345419

- 118725
2016 Buick Envision

Rigth product, on time delivery, I recommend this store 304950

- 118725

Excellent product. Thanks 293583


Ask the Experts about this Tekonsha Custom Fit Vehicle Wiring

Do you have a question about this Custom Fit Vehicle Wiring?

  • Is Tow Package Standard on 2017 Buick Envision?
  • The 2017 Buick Enclave's tow package is not a standard feature on the vehicle, it is optional. As you noted, both of the 4-flat harnesses we offer, the Curt # C56364 and T-One # 118725 require the car to have the tow package in order to work. I've added links to videos of installs and reviews of both harnesses for you to take a look at.
    view full answer...

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Info for this part was:

Edited by:
Lindsey S
Video Edited:
Joshua S
Installed by:
Cole B
Written by:
Alexander C
Test Fit:
Brent H
Updated by:
Hannah L
Updated by:
Isabelle B

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