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

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

Item # 118790

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Custom Fit Vehicle Wiring

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118790 - Custom Fit Tekonsha Trailer Hitch Wiring
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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 118790 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 (11)
  • Videos (2)
  • Photos
  • Why etrailer?

Tekonsha Custom Fit Vehicle Wiring - 118790

  • 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 point in rear cargo area
    • Plug in T-connector
  • 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: 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 inside your trunk, behind the rear interior trim panel on the driver's side of the rear cargo area. You will need to remove access panels, threshold, trunk floor panels, and trays to access the harness. Once you've plugged in the T-connector, pull back the interior trim panel on the driver's side and locate the ground stud. Loosen the bolt, place the screw eyelet on the stud and re-tighten the bolt.

Once installation is complete, the 4-way flat 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 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.

118790 Tow Ready T-1 T-Connector - 4 Wire - Modu-Lite

118790 Installation InstructionsInstallation Details 118790 Installation instructions

This Product Fits The Following Vehicles

2019 - 2020 Subaru Ascent

2019 - 2020 Subaru Ascent

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 T-One Vehicle Wiring Harness Installation - 2019 Subaru Ascent

Today, in our 2019 Subaru Ascent, we're going to be installing Tekonsha's T-One vehicle wiring harness with four pole flat trailer connector. This is what our wiring looks like when it's installed. You might be asking yourself, "Well, I don't see any wiring." That's because it's hidden beneath our storage compartment here and ready to use whenever you need it. When you're ready to use it, you just want to drap it over the back. You want to make sure that you stay away from the striker here in the middle, and it's just going to pinch between our weather stripping. That's fine because it's not going to cause any damage to it.

It's going to compress it and keep it in place. We can now make our connection to our trailer and hit the road.This is going to provide you with your left turn signal, right turn signal, tail lamps and brake lamps. It'll be DOT compliant in all states. On the end of our connector here, you're going to have a dust cap that can help keep out any dirt, debris, and moisture, ensuring a long-lasting connection. You can also use the dust cap to secure it to your hitch's safety chain loops.

Now, on our hitch here, we also have that hidden. It is behind the panel here. If you had a down hanging hitch that wasn't hidden, it would be much easier. You simply slide that through your safety chain loop and secure it like that.One of the biggest benefits of this kit is that it's simply plug and play. There's no cutting or splicing required, and the module that comes included with it will help protect your vehicle from any faults that may occur on your trailer.

If you have a short that happens on your trailer, the module will just shut it down and it won't cause any failures with the lights on your vehicle.We'll begin our installation here at the back of the vehicle. We need to remove our storage cover. We can just sit this one up. That'll be fine. The cross strip that runs across the back side here, we're going to need to just pull that up and separate it.

Now we can remove the entire tray here. We're just going to pull upwards, releasing it, and we'll set this aside. We can now plug our harness in. You'll find your factory connector here, so we'll take the harness from our kit and plug it right in. We'll now need to connect our ground stud. We're going to hook it on the screw located right here. We'll remove the bolt with a 10 millimeter socket, slide our ring terminal on our white ground wire, reinstall the screw, and now we can plug in our tester and verify everything's working properly.If you need a tester, you can pick one up here at etrailer.com, or you can just plug it into your trailer. You want to make sure that you have your left turn signal, right turn signal, tail lamps, and brake lamps. With everything working properly, we can now secure our module. We'll take the double-sided adhesive that comes in our kit. We're going to peel off one side, stick it onto our module, pull the backing off of the other side, and we're just going to adhere it to the wall back here. And we're just going to hold it there for about 20 seconds to make sure that it stays secure.We'll use some of the zip ties in the kit to clean up our wiring. When we put our panel back in, we just routed it out the driver's side corner here and it will live inside of your rear compartment here when not in use. You can just wind it up and push it off to the side, and you're all done. That completes our installation of Tekonsha's T-One vehicle wiring harness with four pole flat trailer connector on our 2019 Subaru Ascent.

Customer Reviews

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector - 118790

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.

- 118790

The hitch came quickly and installed easily. I have a 2020 Subaru Ascent the hitch was listed for a 2019, and fit the 2020 perfectly. Very happy with the result. Need to add the quick release clips for the body panel cover so that the cover can be removed quickly to expose the hitch. Videos and instructions were very helpful. 720299

- 118790
2019 Subaru Ascent

Great step by step videos helped me get the job done in less than an hour. 670710

- 118790

Easy too install and is out of the way. 651492

- 118790

Everything proceeded without a hitch! Pun intended. Product arrived on time, and installation was exactly as outlined. Video instruction was helpful as well. 647169

- 118790

We sold a GO to a customer and needed to wire their 2019 Subaru Ascent to tow. 636488

- 118790

Easy to install and Fits like OEM stand ing 629400

- 118790

Everything was delivered timely and good quality. 619528

- 118790
2019 Subaru Ascent

The 118790 wiring harness and the online video made the installation easy. 616649

- 118790

Arrived quickly with my hitch and, after watching the video (A must!), it installed very easily and quickly with no surprises! This can easily be installed with just the tool needed for attaching the ground wire. 615359

- 118790

Good price/value compared to other options. Was very easy to install. 611521


Ask the Experts about this Tekonsha Custom Fit Vehicle Wiring

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

  • Comparing Draw-Tite and Curt Trailer Hitches for 2019 Subaru Ascent Touring
  • The benefits of the Draw-Tite Trailer Hitch # 76253 that fits your 2019 Subaru Ascent Touring are that it has a concealed crosstube and also that it has a 750 lb tongue weight, which is the highest capacity tongue weight for any hitch that fits your vehicle. That said, the tongue weight will not come into play when you are using your bike rack and it is unlikely to be a factor for a tent trailer. The Curt Trailer Hitch # C13400, which will also fit a Touring model of '19 Ascent, has...
    view full answer...

  • 2019 Subaru Ascent 4-Way and Brake Controller Install Kit
  • Your 2019 Subaru Ascent should have came with a 7-way installed at the rear of it if it came with the factory towing package. Since you are having a hitch installed currently and looking at wiring you most likely do not have the towing package and would need to install the correct wiring. You have to start with a 4-way for this like the # 118790 as this will be the base for the 7-way conversion needed to install and use the brake controller. Since normally this 4-way kit stores in the rear...
    view full answer...

  • Trailer Hitch, Brake Controller, and Wiring Recommendation for 2019 Subaru Ascent
  • Since you don't have a trailer hitch or wiring on your 2019 Subaru Ascent, I recommend the Draw-Tite Max-Frame Trailer Hitch Receiver - Custom Fit - Class III - 2" # 76253 for the strongest hitch and then the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118790 which has a higher amp rating than the alternative options. It is an easy install and then I recommend using the # ETBC7L and the Curt Echo # C51180 for a brake controller and wiring option that doesn't require...
    view full answer...

  • Trailer Hitch Recommendation for 2019 Subaru Ascent
  • Yes, for your 2019 Subaru Ascent the Draw Tite hitch part # 76253 is a confirmed fit and would work well for you. It is a 2 inch hitch which is the most popular size and has plenty of towing capacity at 5,00 lb trailer weight. For trailer wiring you'd then want the part # 118790.
    view full answer...

  • Does The Impact Structure/Bumper Beam Need To Be Removed To Install Hitch on 2019 Subaru Ascent
  • Yes, both the Draw-Tite hitch part # 76253 and EcoHitch part # 306-X7381 require removal of the impact structure. Since both the Draw-Tite and EcoHitch are concealed cross tube designs the impact structure must be removed to make room for the cross member of the hitch. Curt hitch part # C13400 for the 2019 Subaru Ascent does not require removal of the impact structure because it is installed below the bumper. I recommend the Draw-Tite hitch part # 76253 because the cost is less expensive...
    view full answer...

  • Can the Draw-Tite # 76253 Trailer Hitch be Used to Tow a Pop Up Camper with a 2019 Subaru Ascent
  • Yes! The Draw-Tite Max-Frame Trailer Hitch Receiver # 76253 is an excellent option for towing a pop up camper with your 2019 Subaru Ascent. You will need some additional items to tow your pop up camper. I took a look at the online version of your owner's manual and it states that your Ascent is only capable of towing a trailer up to 1,000 lbs if it doesn't have brakes. If your Ascent has the air-cooled continuously variable transmission fluid cooler then you can tow up to 5,000 lbs...
    view full answer...

  • Does Draw Tite Trailer Hitch for 2019 Subaru Ascent Have Capacity for Towing
  • I certainly understand the concerns you mentioned for the Draw Tite hitch # 76253 which fits your 2019 Subaru Ascent but Draw Tite rigorously tested the capacity of this hitch and found it has a towing capacity of 5,000 lbs and a tongue weight capacity of 750 lbs. Draw Tite is normally very conservative with their capacity figures as well and tends to err on the side of caution always in this regard. As long as you plan to tow under the capacity of this hitch and your vehicle you will be...
    view full answer...

  • Trailer Hitch and Wiring for 2019 Subaru Ascent and Should Weight Distribution be Used
  • If the manufacturer of the vehicles states that you can't use a weight distribution system then you should not use it. They designed the frame of the vehicle and are the authority on whether or not it could handle the additional stress of a the system. I'd recommend finding a trailer that is under the towing capacity of your 2019 Subaru Ascent and then installing the Draw Tite hitch part # 76253 you referenced which would give you a 2 inch hitch that fits behind the rear bumper panel. I...
    view full answer...

  • Installing a Tekonsha Primus IQ Brake Controller on 2019 Subaru Ascent
  • The photo you sent looks like it may be what you need to hardwire to the Tekonsha Primus IQ Trailer Brake Controller # TK90160 to as a step of the installation. To install this brake controller in your 2019 Subaru Ascent without the factory tow package you need to start by adding a 4-way, the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118790; I have added a link to an installation video of this connector on a '19 Ascent for you to take a look at. You will also...
    view full answer...

  • Can I Really Tow 5,000 lbs With My 2019 Subaru Ascent
  • The Draw-Tite hitch part # 76253 for 2019 Subaru Ascent is rated for towing up to 5,000 but only if the Subaru is equipped with an air-cooled continuously variable transmission fluid cooler from the factory and the trailer has brakes. The owner's manual states vehicles without the variable transmission fluid cooler can tow up to 2,000 lbs. It is a good idea to check to make sure your Subaru Ascent is equipped with the cooler from the factory before towing 5,000 lbs. You can find out...
    view full answer...

  • Compatibility of Weight Distribution System on 2019 Subaru Ascent
  • When towing a trailer your 2019 Subaru Ascent owners manual doesn't state anything about not using a weight distribution system. It does give clear guidelines for tongue weight and trailer load that need to be followed for your warranty, but using a weight distribution system is not mentioned in the online version. It does mention distributing the weight of your trailer to make sure it is even. I do recommend using a weight distribution system for your trailer to help with the way...
    view full answer...

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Info for this part was:

Edited by:
Lindsey S
Installed by:
Jeff D
Video Edited:
Jacob T
Video by:
Dustin K
Written by:
Alexander C
Updated by:
Hannah L
Updated by:
Isabelle B
Test Fit:
David F

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