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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 # 118790
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Custom Fit Vehicle Wiring

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T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector Custom Fit 118790
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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. 1-800-940-8924 to order Tekonsha custom fit vehicle wiring part number 118790 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 (77)
  • Q & A (0)
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  • Why etrailer?

Tekonsha Custom Fit Vehicle Wiring - 118790

  • 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 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

Installation Details 118790 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 - 118790

Average Customer Rating:  4.9 out of 5 stars   (77 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.


Great product. Works perfect and was very easy to install and disappears when not in use.


Very helpful staff. I had trouble with the shipping companies which sent the order to the wrong location, not etrailer's fault. The team at etrailer resolved the shipping issue. I am satisfied with the merchandize I received, etrailer stands behind their products and were helpful in selecting the right combination of components. Great company, great phone service!


Easy install. Bought this with the Curt Class III hitch. All components match up and install without a struggle. The Tekonskha Custom Fit harness incorporates turn signals, running lights and brake lights.


Everything I have Bought from etrailer has been exactly correct and what I needed. George J and the team are always helpful and the videos are great.


This worked well on my 2020 Subaru Ascent. The only reason for 4 stars instead of 5 is due to there not being a clamp or something to hold the final cable in place. It isn’t a big deal, you can tuck it into the bumper and that seems to be fine but would have liked a better setup there. Overall great harness and pretty easy to install.

2022 Subaru Ascent

Very easy installation, I followed the video online and got it down very quickly.
Great instructions and installation!

Ford Flex

What you see is what you get. Works perfectly. Instead of leaving it laying in the cargo bin i ran mine through the grommet for the tail light over the bumper and on to the hitch. That was a bit of a struggle with the size of the cap since it didn't flex very well but not major. Arrived ahead of expected shipping date with everything needed to install.

2020 Subaru Ascent

Product was as described. It fit perfectly on my 2020 Subaru Ascent an was very simple to install the hitch and harness. Took about about 75 minutes. Products were high quality. Also saved about $700.00 if a Subaru dealer installed. When not in use it is totally concealed by the center removal bumper face plate.

Highly recommend this product.


Very easy to install. The only difficulty is actually getting to the place where the harness is to be placed. Instructions are easy to follow and, with a little care, the system can be installed with no issues.

Still working very well.
Bruce - 08/24/2021


Instructions were clear and easy to understand so much so I had my 14 year old son install this unit.


I purchased this for my 2019 Subaru Ascent along with a Drawtite hitch 76253 and a brake controller with a dash mounted control knob so that the actual controller is hidden near the steering wheel shaft hidden under the dash. All three items were installed and we enjoyed a great summer of RV trailer camping in the summer of 2019.

I had an RV service professional install it because I am too claustrophobic under my Ascent and I am very happy that it is hidden behind with only the control button visible and it works great!
John - 05/01/2021


Great product! Ease of installation. Super fast shipping. Definitely recommend for all your truck and trailer needs.


I was impressed with the installation service, the finished appearance and the price.

Its great!
Paulette W - 01/03/2022

2020 Subaru Ascent

Easy installation, the wiring options video helped me pick out what was best for me and item came with everything needed.

2020 Subaru Ascent

I have been using for several years on multiple vehicle hitch and wiring projects and I have always been very pleased with the product and my experience. This time was no different. I needed to install a hitch and wiring harness for a 2020 Subaru Ascent. The parts that were matched with my vehicle online fit perfectly. The instructional videos that accompany every part are outstanding. Each step is clearly explained and easy to follow. Once again, delivered exceptional service, prices, parts, delivery, and everything else I needed to complete my hitch and wiring project in just a few hours. I highly recommend and I will continue to be a customer for several decades to come.


Great experience. Currently deployed and wanted to get my wife a hitch for her new Ascent. The Subaru dealer really screwed up everything but Arthur at ETrailer saved the day. Super friendly and helpful. Fast shipping and got exactly what was ordered! Highly recommend.


Works perfectly. Easy install.


Super easy to install and still working a year later


The install was straight forward. If I hadn't been also installing a trailer brake controller the entire install would have taken all of 15-20 minutes. Very simple!


Worked great


Super easy to install.


I haven’t installed it yet but the how videos makes me believe it will be simple. Great web site for ordering and quick shipping.


Works great fit perfectly.


etrailer is always helpful. This is exactly what I needed and works perfectly.


Works great super easy install .

Show More Reviews

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

  • Hitch Recommendation for 2020 Subaru Ascent that Fits Behind Bumper Panel
    We do have hitches that fit behind the bumper of your 2020 Subaru Ascent. The one I recommend is the Draw Tite part # 76253 as it fits behind your bumper like you want and is also priced the best. I attached a picture of what it looks like installed as well as an install video for you to check out too. For trailer wiring then the kit I recommend is the # 118790 which installs very easily and also comes with a very reliable converter box so it will last a long time!
    view full answer...
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  • 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...
  • 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...
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  • Recommended Trailer Wiring Harness For 2020 Subaru Ascent
    The Draw-Tite Max-Frame Trailer Hitch Receiver # 76253 you were looking at for your 2020 Subaru Ascent does not include a 4-way wiring harness so you will need to purchase one separately. I recommend Tekonsha T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118790 which is a plug and play harness confirmed to fit your Ascent, and will give you the 4-way trailer connector you are looking for. To complete your towing setup you will also need a ball mount, hitch ball, and...
    view full answer...
  • Comparing the Best Hitches for the 2020 Subaru Ascent
    The biggest difference between the Draw-Tite Max-Frame Trailer Hitch Receiver - Custom Fit - Class III - 2" part # 76253 and the Curt Trailer Hitch Receiver - Custom Fit - Class III - 2" part # C13400 is going to be how they look when installed. The DrawTite has a look extremely similar to the factory style hitch. It sits behind the factory hitch cover and is not visible at all when not in use. The Curt will sit below the rear bumper cover and has an exposed cross tube and receiver tube...
    view full answer...
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  • Does Draw-Tite Trailer Hitch 76253 Increase Tongue Weight Rating Of 2021 Subaru Ascent?
    Based on what information I was able to find on your 2021 Subaru Ascent you will be limited to 500lbs tongue weight if you have the air-cooled continuously variable transmission fluid cooler, and 200lbs if you do not. In either case you will be limited to the lower rating between the vehicle and the trailer hitch receiver, in this case the Draw-Tite Trailer Hitch Receiver # 76253 you were looking at. Since both ratings of the vehicle are lower than the rating of the hitch, you would be...
    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...
  • Does Curt Trailer Hitch Receiver C25VR Fit 2022 Subaru Ascent Onyx Edition
    I checked with the manufacturer, Curt, for you and can verify that yes, the Curt hitch does fit your 2022 Subaru Ascent Onyx Edition: - Curt Trailer Hitch Receiver # C25VR This will give your Ascent a nice option for a hitch that can be concealed, and the only other thing you will need, if you plan on doing some towing with your '22 Ascent, is a trailer wiring harness. The best option for a harness, due to it being the most reliable, is from Tekonsha, the T-One Vehicle Wiring Harness...
    view full answer...
  • Can 2021 Subaru Ascent With Curt Trailer Hitch Use Weight Distribution
    That's a good question, and the short answer is yes, you can use a weight distribution hitch with the Curt hitch that fits your 2021 Subaru Ascent: - Curt Trailer Hitch Receiver # C25VR I took a look at the owner's manual for the 2021 Subaru Ascent, and it is referring to the factory hitch in regards to not using weight distribution. The reason is, that hitch is not rated for use with a weight distribution system, but the Curt # C25VR rated for use, which is why you can use it for that. The...
    view full answer...
  • 7-Way and 4-Flat Connector for a 2020 Subaru Ascent
    Yes, we do have a wiring harness that has both a 7-way and a 4-way for your 2020 Subaru Ascent. However, you will need a 4-way connector on your car before this will work though. I recommend the Tekonsha T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector item # 118790. This harness plugs in to existing wiring to provide a 4-flat connector. The 7-Way and 4-Way all in one connector you referenced is the Universal Installation Kit for Trailer Brake Controller - 7-Way RV and...
    view full answer...
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  • Is etrailer Hitch for 2021 Subaru Ascent Safe to Tow With
    We've sold quite a few of the etrailer hitch part # e55ZR that fits your 2021 Subaru Ascent and none of our customers have had an issue with the hitch when towing. It was extensively tested and the way it installs is a safe and secure place on the vehicle. There are several other hitches that install the same way for different vehicles and it works fine. I would not worry at all as long as you plan to stay under the weight capacity of the vehicle. For trailer wiring then the Tekonsha kit...
    view full answer...
  • 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 a...
    view full answer...
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  • 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...
  • 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 need...
    view full answer...
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  • Recommended Hidden Hitch and Wiring For 2020 Subaru Ascent
    The Curt Trailer Hitch Receiver 2" part # C25VR is a fit for the 2020 Subaru Ascent. The Curt hitch is hidden behind the removable fascia panel at the rear the Subaru. When the hitch is not in use the panel can be replaced for a completely hidden clean OEM look. I have attached a photo for your reference. If you plan on towing a trailer you will need wiring. For that I recommend T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # 118790. The Tekonsha wiring is more reliable...
    view full answer...
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  • Trailer Connector/Wiring Harness for 2021 Subaru Ascent
    The correct wiring harness needed will depend on the type of trailer you're wanting to pull. If you're pulling something basic like a small utility trailer and only need a 4 pole trailer connector, the # 118790 would be what you need. However, if your trailer has a 7-way trailer connector, you'll need the # 118290.
    view full answer...
  • Recommended Hitch for a 2022 Subaru Ascent that Fits Behind the Removable Bumper Panel
    The hitch that I recommend for your 2022 Subaru Ascent is the etrailer Trailer Hitch Receiver # e55ZR. This hitch is made in the USA, has a bolt-on, no-drill installation and will provide you with a 2" receiver which is the most common size used for hitch mounted accessories such as bike racks, cargo carriers and ball mounts. This hitch will also mount behind the bumper and you can access the hitch receiver by removing the bumper panel like you were looking for. If you plan to do any towing...
    view full answer...
  • What is the Difference Between the Draw-Tite 76253 and Curt C25VR for 2020 Subaru Ascent
    There are some slight differences between the Draw-Tite # 76253 and the Curt # C25VR, but it's mostly down to the quality of the powder coat on the two hitches. The powder coating on the Curt hitches is traditionally applied a bit thicker and is a better quality, in my opinion. This is going to translate to less dings and scratches and generally means that the hitch is going to be less susceptible to corrosion over the long term, so I do recommend going with the Curt # C25VR hitch for your...
    view full answer...
  • What Will be the Best Brake Controller for My 2022 Subaru Ascent Without Factory Tow Package
    The brake controller I recommend for your 2022 Subaru Ascent is the Tekonsha Prodigy iD Trailer Brake Controller - Bluetooth - 1 to 4 Axles - Proportional # TK49VR. The reasons I recommend the Tekonsha Prodigy iD is because you will not have have a controller underneath your dash, instead you will have a knob mounted on your dash or console. Also, this brake controller is blue-tooth enabled, allowing you to use your phone as a brake control interface. To connect your brake controller you...
    view full answer...
  • Recommended Hidden Style Hitch And Wiring For A 2022 Subaru Ascent
    I will start by saying that the Anderson Rapid Hitch # AM3414, though a little overkill, is definitely a good adjustable ball mount and it will serve your needs well. To get a hitch that will handle this and still be hidden once installed on your 2022 Subaru Ascent, you will want to look at the Curt # C25VR. This will a bit of a difficult install as it will require taking the back of the vehicle apart and replacing the bumper beam with the hitch, but it will allow you to use the factory...
    view full answer...
  • What is the Difference Between the Curt and Draw-Tite Hitches for a 2020 Subaru Ascent
    The Curt # C25VR and Draw-Tite # 76253 will actually be very similar to each other. Both will install the same way and will be completely hidden once completed due to the removable panel on the bumper fascia. However, there are a few differences. The Draw-Tite # 76253 will have a bracket welded on the cross tube where the Tow Ready Mounting Bracket 4-Pole Flat # 18144 can be bolted to. This makes mounting a wiring harness, like the Tekonsha T-One Vehicle Wiring Harness with 4-Pole Flat...
    view full answer...
  • What Is The Least Visible Trailer Hitch Available For A 2022 Subaru Ascent
    If you are in need of getting your 2022 Subaru Ascent set up for light towing and carrying a bike rack, we definitely have what you need. I recommend going with the Cust Fit Class III # e55ZR. This American made hitch, though fairly involved, requires no drilling or trimming to get installed. It also has a 5,000 pound towing capacity and a 750 pound tongue weight capacity, though you will need to confirm what your vehicle can handle in the owner's manual. The big reason I am...
    view full answer...
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  • 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 if...
    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...

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Info for this part was:

Employee Lindsey S
Edited by:
Lindsey S
Employee Jeff D
Installed by:
Jeff D
Employee Joshua S
Video by:
Joshua S
Employee Dustin K
Video by:
Dustin K
Employee Jacob T
Video Edited:
Jacob T
Employee Chris R
Video Edited:
Chris R
Employee Wilson B
Updated by:
Wilson B
Employee Hannah L
Updated by:
Hannah L
Employee Isabelle B
Updated by:
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Employee Alexander C
Written by:
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Employee David F
Test Fit:
David F
Employee Ryan G
Test Fit:
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