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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 # 118591
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Custom Fit Vehicle Wiring

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Tekonsha Trailer Hitch Wiring - 118591
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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 118591 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.
  • All Info
  • Reviews (10)
  • Q & A (0)
  • Photos
  • Why etrailer?

Tekonsha Custom Fit Vehicle Wiring - 118591

  • 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 in trunk
    • Plug in T-connector
    • Run 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: 2.1 amps per circuit
    • Tail lights: 5.6 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 trunk, behind the tail lights on both the driver's side and passenger's side. You will need to remove some interior trim or carpeting to access the harness. Once you've plugged in the T-connector, run the hot lead with the attached fuse holder to the car battery in your trunk. 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 within your trunk.

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.

118591 Tow Ready T-1 T-Connector - 4 Wire - Modu-Lite

Installation Details 118591 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 - 118591

Average Customer Rating:  4.9 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.

2014 Lincoln MKZ

Ordered this after finding out the CURT version literally is not wired correctly and they refuse to fix their design. The CURT one will not give you brake lights, and the left running light stopped working when I tried to just live with it. I ordered the Tekonsha kit after seeing all the positive reviews and it instantly worked perfectly. Now all my trailer lights work as they should.

2017 Lincoln MKZ

So far everything is fine. One thing surprised me - that the trailer brake lights only work when the car is running. The trailer running lights - like the car rear lights do not work - but the directional and brake lights do when the switch is in the running light position. When the switch is in park or headlights everything is good.

Thanks for the follow-up. It is not uncommon for this to happen if the key is not in the on position. As long as all the functions are working properly when the key is on you are good to go. It is possible that the vehicle is not sending the brake signal with the key in the running light position.
-- Etrailer Expert Rachael H - 05/21/2018
Everything is fine.
Richard - 05/20/2019

2013 Lincoln MKZ

After trying 2 from a well known manufacturer, it was apparent that the design was not compatible with my 2013 Lincoln MKZ. Offered me to BUY a universal kit.Then, either graft on the plugs from the kit I had or splice in all the connections. Even though the unit was designed for this car. Searched and found one and after checking 9 vendors, etrailer appeared to have one.. right model, no inventory. Manufacturer would not give etrailer info on when they might get one. Worked with PatC in CS. She knew here stuff. Recommended another manufacturer. Assured me it would work as they had just installed one on another Lincoln. Three days later it came . 45 minute install. It works!


This order replaced a wiring system and module that came the the hitch when it was first installed about 3 year ago. Failure mode was that fhe original "control module" failed to pass the correct voltage to the tail lights (too low to light the bulbs).
This replacement (at a cost of about $xx.xx) has been installed and all work properly. The new part fit perfectly, and functions just as it should.
Hopefully this sealed "module" will last longer.
This has been a very good company to deal with.


I installed the T connectors easily without any problems. I found the instructions and set-up for the main power to be complete but very tedious. I determined for my use (bike rack and occasional towing) that I would be better off getting power from a portable battery source so I set up with a cigarette lighter plug.

2016 Lincoln MKZ

Received very quickly. very easy install on tow package and plug directions were very easy to follow thanks for a great deal




2018 Lincoln MKZ


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

  • Recommended Towing Setup for a 2017 Lincoln MKZ Hybrid
    Yes, the automatic transmission in your 2017 Lincoln MKZ Hybrid is capable of towing a trailer. According to your owner's manual your vehicle has a maximum towing capacity of 1,000 lbs. Therefore, as long as your U-Haul trailer is less than 1,000 lbs. then you can safely tow it. In order to tow a trailer with your vehicle you will need a trailer hitch, wiring harness, and ball mount/hitch ball. For this, I recommend the Draw-Tite Sportframe Trailer Hitch Receiver part # 24897, the T-One...
    view full answer...
  • Replacement Hardware Kit for Curt Hitch C12091
    Yes, we do have replacement hardware for your Curt Trailer Hitch Receiver item # C12091. It is the Replacement Hardware Kit for Trailer Hitches item # RHK. You will want to go to that product page and on the right side you will want to put in Curt for the manufacturer and C12091 for the Hitch item Number. This will get you a new set of hardware for your 2018 Lincoln MKZ. I linked a couple of installation videos on an older model MKZ. If you are in need of a wiring harness to control your...
    view full answer...
  • 2 Inch Ball for a Class I Trailer Hitch and Ball Mount for a 2013 to 2016 Ford Fusion or Lincoln MKZ
    Yes you can use a 2 inch ball with the appropriate ball mount (# 3594) with trailer hitch # 24897. The 2 inch ball is # 19258. I have included a link to a video showing an example installation of the hitch for you. This hitch is designed for the 2013 to 2016 Ford Fusion and Lincoln MKZ. For a trailer wiring harness that fits the Fusion I recommend # 118574. And for the Lincoln MKZ I recommend # 118591. I have included links to videos on both harnesses for you.
    view full answer...
  • Hitch and Towing Accessory Fits for 2014 Lincoln MKZ Hybrid
    The Draw-Tite has completed test fitting and has confirmed that the # Draw-Tite 24897 does indeed fit the 2014 Lincoln MKZ. The hitch is confirmed as being a fit for Hybrid models. If you'll be doing some light duty towing, you might also need the following: Ball mount, part # 3594 Trailer wiring harness w/ 4-pole trailer connector, part # 118591 2 inch trailer ball, part # 19258 1-7/8 inch trailer ball, part # 19256 Locking hitch pin, part # RH2-XL
    view full answer...
  • Trailer Hitch Recommendation for 2017 Lincoln MKZ that Allow Reinstallation of Lower Fascia
    For the Curt hitch part # C12091 for your 2017 Lincoln MKZ Curt decided to recommend removal of the lower fascia instead of trimming it and reinstalling it. They don't have recommendation on how to trim the fascia to get the hitch to fit but I am sure that if you wanted to come up with a way to trim it like the Draw Tite part # 24897 I am sure you could pretty easily. That being said I would recommend the Draw Tite over the Curt because the Draw Tite does not require the use of a stabilizer...
    view full answer...
  • Recommended Tow Bar Wiring Kit For A 2017 Lincoln MKZ
    When it comes to installing the tow bar wiring on your 2017 Lincoln MKZ The Roadmaster 4-Diode Universal Wiring Kit for Towed Vehicles - 7-Wire to 6-Wire Straight Cord # RM-152-98146-7 is the correct kit you would need. This kit is for a RV with a 7 round adapter and will make the Lincoln MKZ mirror the turn, stop and tail lights of the motor home. If your motorhome has a 4 flat connector you would need The Roadmaster Universal Hy-Power Diode Wiring Kit # RM-154. The # 118591 is used...
    view full answer...

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Info for this part was:

Employee Lindsey S
Written by:
Lindsey S
Employee Jeff D
Installed by:
Jeff D
Employee Jacob T
Video Edited:
Jacob T
Employee Kathleen M
Video by:
Kathleen M
Employee Laura H
Updated by:
Laura H
Employee Wilson B
Updated by:
Wilson B
Employee Alexander C
Updated by:
Alexander C
Employee Isabelle B
Updated by:
Isabelle B
Employee Jared G
Test Fit:
Jared G

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