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

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

Item # 118643
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Custom Fit Vehicle Wiring

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Tekonsha Trailer Hitch Wiring - 118643
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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. 1-833-496-1390 to order Tekonsha custom fit vehicle wiring part number 118643 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 (172)
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Tekonsha Custom Fit Vehicle Wiring - 118643

  • 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
  • Includes ModuLite power module to ensure that your vehicle's wiring matches that of your trailer
    • Powered module connects 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.

118643 Tow Ready T-1 T-Connector - 4 Wire - Modu-Lite

Installation Details 118643 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 - 118643

Average Customer Rating:  4.8 out of 5 stars   (172 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.


The hitch fit as expected, but two holes needed to be tapped in order for the hitch to fit correctly. The wiring harness suggested worked as it should. I am happy with the hitch so far. My only hesitation from 5/5 stars was having to do additional tapping to get it to fit my vehicle. Luckily I had the necessary tools on hand.

Ford Transit Connect

I have had to install several hitches for two of my ford transit vans they don’t come with tow packages. I purchased the electrical connectors and hitches from E-trailer and was able to wire up my Vehicles. they had the right part with easy video instructions great company highly recommend E-trailer.


Good kit. Good instructions. Pretty straight forward install. Only problem: the wire that must be run all the way to the engine compartment for battery power was about a foot or two too short! I wouldn’t buy again just for this reason. What a hassle to have to splice in addition wire and heat shrink. Otherwise works fine.

Running the power wire to the battery can be challenging depending on the vehicle. We do have a FAQ that can help. Please see the link below.
-- Etrailer Expert Jenny N - 07/14/2022

2018 Ford Transit T250

Although, I have not had time to install the hitch and wiring harness, your company provided excellent service.


Easy fit and very simple. I will say it is a bit difficult to get the triangle shaped bolts to tap in and stay square

2017 Ford Transit T250

Very fast service. I ordered hitch and harness on Monday and it came Thursday. Everything looks great.

Ford Transit Connect

This was exactly what I needed for my full size transit van - Fairly easy install, but needed the power line to be about 3feet longer. Easiest way would be to put on a lift, but local garage did not have enough height to lift, so crawled my way under & attached power line with rubber tubing on every possible rub line. I may have woven the power line through too many attachment points, but never wanted to go back under to fix. I ended up about 2 feet short of my power source at the front, but heat shrunk a attachment to additional wire of same gauge and it works fine. Very pleased with purchase - 4 star due to short wire on the power side, but everything else was simple plug in - routed wires under he back sill plate for clean installation. Oh, suggest you have lots of wire ties available before starting this project.

2020 Ford Transit T250

Instructions not very clear. Wiring harness is great

2020 Ford Transit T250

Couldn’t get any simpler. I am very pleased with the quality of the product. It arrived as expected with all the items. I watched the installation video and went to work. It took approximately 1hr of crawling under the van but it’s well worth it. Only thing I’m missing is the bracket that mounts the 4way to the hitch. I’ll purchase that and be ready to roll!


This product is great, and the etrailer video for the installation is terrific. I may have gotten it installed without the video, but it was very simple to follow along as an expert did it. Absolutely the only challenging part of this installation is getting under the car to run the 12V wire upfront, and that was just the physical challenge of getting on the ground so many times.


As expected snd accorfing other install ers


Good product. Good instructions.


After a year it has been a solid hitch. The installation was straight forward. The video was extremely helpful. I would definitely recommend it to a friend!


It’s great, I have a no problem after install etrailer wire product.

2016 Ford Transit T250

Good product. easy to install, instructions made sense the only very minor thing is that the wire from the hitch to the + battery terminal is maybe 12 inches too short to be convenient for the extended length transit.

2015 Ford Transit T250

Lighting kit was very easy to install. I watched the video first, which was very helpful.

I havent used it a lot, but dont expect any disappointments from it.
Ray - 09/05/2021


I didn't get the wire harness I had initially ordered. I called and spoke to one person and he immediately responded and sent me the missing harness which I easily installed. I am very satisfied with the prompt and direct service you company provided

2019 Ford Transit T250

Because of the great installation video, I was able to install this in about an hour. etrailer does a fantastic job educating customers.

2016 Ford Transit T250

showed up early and install was easy

2020 Ford Transit T350

Everything fit well and was going just as the installation video showed until I got the power cable to the motor (from underneath the van) and realized it was no where near long enough for my 148WB. Needed at least another 5'. Ended up having to remove the drivers taillight again and fished the cable inside the van from there and ran it right to the battery under the seat.

Thank you for your review. The wiring has to be installed exactly as the instructions say or there will not be enough wire. Extra wire purchased will have to be cut and spliced in.
-- Etrailer Expert Sierra K - 07/22/2021

2018 Ford Transit Connect

Just recieved , having installed yet . Don’t foresee any issues installing under a 2018 Transit that will pull a 5x10 that I’m presently welding up. Typical good service with helpful etrailer install video and peer review input. Thanks for concern. No pics yet,


Worked great and easy to install for the most part. Running the power wire is the hardest part having to squirm under the transit do often. Lol I did change one thing from the install vid for my 2016 Transit. I connected the power wire to the second terminal so I didn’t have to modify the cover like the video suggests. It just unclips front and back and then snaps back on. See pix.


Very good price and prompt delivery


Works as described, shipping was on poi nt.


This was a real easy installation of the wiring hardware

Show More Reviews

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

  • Trailer Wiring Harness Recommendation for 2017 Ford Transit T350
    Yes, for your 2017 Ford Transit T350 the Tekonsha kit part # 118643 is the correct fit and would work well. I attached an install video for this for you to check out as well.
    view full answer...
  • Tekonsha T-One Wiring Harness Installation on 2016 Ford Transit T150
    I did some research on the engine compartment of your 2016 Ford Transit 150 and there are actually a couple of ways you can install the Tekonsha T-One Vehicle Wiring Harness # 118643. The installation video you referenced where the side wall panels were removed in order to route the power wire to the battery under the driver's seat is one method. Since you are unable to remove the wall panels in your vehicle, I instead recommend running the power wire out and along the underside of the...
    view full answer...
  • Recommended Trailer Wiring Harness for 2019 Ford Transit T250
    For your 2019 Ford Transit T250 I highly recommend the Tekonsha T-One Vehicle Wiring Harness # 118643, which will plug right into existing ports behind the tail lights and features an extremely reliable converter box that has shown itself to be superior to those from other manufacturers. After making those connection behind the tail lights you will also need to run the hot lead up to the Transit's battery for power. This will provide you with a 4-Way connector to connect with and power...
    view full answer...
  • Will Installing the Tekonsha Wiring Harness on my 2020 Ford Transit T-250 Void my Warranty
    The T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # 118643 will not void any warranty you have on your 2020 Ford Transit T250. There was a bill passed that protects consumers from any type of cancellation of warranty when adding aftermarket components such as wiring harnesses. As long as the product you are using did not directly cause the issue there is no voiding that can be done. I have linked an installation video for you if you would like to check it out.
    view full answer...
  • Newest Model Tekonsha Wiring Harness for my 2020 Ford transit T-250
    The Tekonsha T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # 118643 is the newest offering we have from Tekonsha for your 2020 Ford Transit T-250.
    view full answer...
  • Recommended Trailer Wiring Harness for 2020 Ford Transit 250
    For your 2020 Ford Transit 250, I recommend the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118643 for your trailer wiring. The 6 pin connector you referenced is not the correct harness for your trailer wiring. I recommend this wiring harness because it will easily connect to your vehicle wiring behind the taillights without any splicing. This will also draw power directly from the vehicle battery to protect your vehicle electronics.
    view full answer...
  • Which Trailer Connector for 2015 Ford Transit T250
    The connector you'd install will depend on which connector the trailer you're wanting to tow uses. To install a 7-way, use part # 22114, or for a 4 pole trailer connector, use # 118643. Either trailer connector is compatible with all styles of the 2015 Transit T250. I've linked to the installation instructions for both wiring harnesses, and to an install video showing the # 118643 being installed on a 2015 Transit T250.
    view full answer...
  • Parts Needed to Install 7-Way Trailer Connector on 2020 Ford Transit T250
    If your trailer is equipped with a 7-Way but you only need to power its basic signal lights (and not electric brakes) then adding a 7-Way connector to your 2020 Ford Transit T250 will actually be fairly simple. To do this you will need to start with a 4-Way harness. For this I highly recommend the Tekonsha T-One # 118643, which will plug into existing ports behind the driver and passenger side tail lights. Once those connections are made you will run the power wire up to the Transit's...
    view full answer...
  • 4-Way Trailer Wiring Harness that Fits 2019 Ford Transit 350 Dually Extended
    Since you have the dually extended version of the 2019 Ford Transit T350 the 4-way wiring kit you'd need is the # 118722. We had the chance to install this kit on a Transit like yours which I attached an install video link for on this page. The video shows a single rear wheel version but it fits the dually models too.
    view full answer...
  • Recommended Wiring Harness for 2015 Ford Transit T250
    For your 2015 Ford Transit T250, I recommend the Tekonsha OEM Replacement Vehicle Wiring Harness w Brake Controller Adapter - 7 Way Trailer Connector # 22114 which will give you everything you need for a complete tow package wiring. If you just want a 4-way trailer connector, then I recommend the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118643 which connects to the factory wiring behind each tail light. If you use the 7-way harness, I also recommend using the...
    view full answer...
  • Troubleshooting The T-One Vehicle Wiring Harness For Ford Transit T350
    Not to worry, this is a common issue and I will be happy to help you get this issue working. Since you have connected the trailer to another vehicle and the lights work on it, you have isolated the issue to your tow vehicle, which eliminates half of the troubleshooting process. The first step I would take is to use a circuit tester like part # 40376, to test the pins on the connector for proper function. I've attached a video that shows how to test a 4-way trailer connector for proper...
    view full answer...
  • Trailer Hitch and Wiring Harness for 2020 Ford Transit T150 Cargo Van
    Absolutely! First, in order to hook up to the trailer you will need to add a trailer hitch to your 2020 Ford Transit T150. For this I highly recommend the Curt Class IV # C14012, which features a sleek hidden cross tube design so that only the 2" receiver is visible from behind the van (see attached images) and more than enough capacity to handle a smaller trailer. This custom hitch will line right up to existing holes in the frame rails for a simple bolt-on installation and all the...
    view full answer...
    Image 1 for Image 2 for
  • Determining Which Vehicle Wiring Harness Fits 2020 Ford Transit T350HD XLT DRW
    You can determine if your 2020 Ford Transit 350HD XLT DRW you will need to check under the rear bumper for a black connector. If it is not behind the bumper check around the spare tire. Chances are that if you do not have the connector installed, that you do not have the factory tow package. You can also call your local Ford dealer with your VIN and they will be able to tell you every option you vehicle has. If you find your Transit does not have the factory tow package then the available...
    view full answer...
  • Troubleshooting Trailer Taillight Kit that Allows Vehicle Lights to Work but Not Trailer
    Since the vehicle taillights still work that means the connectors are fully seated. Most likely the problem is the converter box of the kit then. What you will want to do is test the wires going into the box of the converter box for voltage with a circuit tester like the # PTW2993 to see if there is voltage going into the box when the taillight functions of your vehicle are applied, and then test the output side of the box to see if the current is making it through the converter. If not...
    view full answer...
  • Replacement Wiring Harness and Brake Controller Wiring for 2016 Ford Transit T350
    On your 2016 Ford Transit T350 it sounds like you have the hardwired 7-way and a damaged brake controller. My recommendation is to replace your wiring with the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118643 and then the # ETBC7 which is recommended for your vehicle. This will work with any brake controller you desire as a replacement. I've linked a page to all your options. This will give you the module you referenced and the circuit breakers needed for a...
    view full answer...
  • Estimate of How Long it Takes to Install Trailer Hitch and Wiring on 2017 Ford Transit T250
    The model of vehicle does impact the time it takes to install a trailer hitch and wiring, although for a 2017 Ford Transit T250 a decent ballpark estimate is 1-1/2 to 2 hours. The good news is there is a very simple to install trailer hitch for a '17 Ford Transit T250 Cargo Van or Passenger Wagon so this will take the least amount of time. The Trailer Hitch # E98842 can be put installed in roughly 30 minutes for an everyday DIYer; it does not require any drilling to install...
    view full answer...
  • Color Code For HopknsINSIGHT Trailer Brake Controller
    I don't think the picture came though, but I can tell you before you continue, that you're going to need to add a 4 way trailer connector # 118643 if you do not have one already, and then you need to add a 7 way connector # ETBC7. From here you can install the HopkinsINSIGHT brake controller. If you have all that the wiring is as follows: the black wire to the positive terminal on your vehicle's battery, the red wire to the cold side of your stop lamp switch or your brake light, the...
    view full answer...
  • Parts Needed to Install Brake Controller in 2017 Ford Transit T150
    You will need to start with a 4-way (if you do not have one) on your 2017 Ford Transit T150. For that you would want the # 118643. From there you would need to convert the 4-way to a 7-way so that you can install the brake controller. For that you will want the Brake Controller Install Kit and 7-Way Adapter part # ETBC7. I attached installation instructions and an install video for this product as well. For a brake controller I would recommend the Prodigy P3 Brake Controller part # 90195....
    view full answer...
  • Does Curt Trailer Hitch C13193 For 2015 Ford Transit Include All of the Mounting Hardware
    I personally went out to the warehouse to check on Curt trailer hitch # C13193. It does include ALL of the hardware including the self-tapping bolts. All of the hardware listed in the instructions, linked for reference, is included. I am not sure where the installer got that information. If you plan on doing some towing you might be interested in etrailer ball mount kit # 989900. It comes with 2 ball mounts; one with a 3/4 inch rise or 2 inch drop and one with a 2-3/4 inch rise or 4 inch...
    view full answer...
    Image 1 for
  • Trailer Hitch and Wiring for a 2015 Ford Transit T250
    The bumper on the Tranist T150 in the video for trailer hitch # C13193 does have a unique design with that cutout in the center. The regular bumper doesn't have that cut out but the hitch is still the same, even for the T250. You will just need to use accessories that clear the rear bumper so it isn't going to be a problem for you at all. For towing you could use an extra long ball mount, like those I have linked, or even a super extra long ball mount, # 80232, which measures 16 inches...
    view full answer...
  • Trailer Hitch and 4-Way Connector for a 2016 Ford Transit T150
    I will be happy to recommend a trailer hitch, wiring, and other parts for your 2016 Ford Transit T150. For a trailer hitch I recommend Curt hitch # C13193. This is a Class III hitch with a 2 inch receiver. It is rated for 900 pounds tongue weight and 6,000 pounds gross trailer weight (8,000 when used with weight distribution). I have included a link to a video showing an example installation for you. To add a 4-Way flat trailer connector I recommend # 118643. It plugs in line with the...
    view full answer...
  • Trailer Hitch and Wiring for a 2016 Ford Transit T250
    For your 2016 Ford Transit T250 I recommend Curt trailer hitch # C13193. This is a Class III trailer hitch rated for 6,000 pounds gross trailer weight. When using weight distribution it is rated for 8,000 pounds gross trailer weight. I have linked a video showing an example installation for you. To add a 4-Way flat trailer connector at the back of the van I recommend wiring harness # 118643. I have included a link to a video showing an installation of the wiring as well. If you plan on...
    view full answer...
  • What Parts Do I Need to Install a Brake Controller in my 2019 Ford Transit T350
    Since you already have the 4 way connector on your 2019 Ford Transit T350, you're well on your way to adding everything you need to install a brake controller. If for some reason your existing plug was damaged and you were to need a new 4 way connector you can use the Tekonsha # 118643, which Tees into your vehicle wiring for an easy installation. You'll then want to add a 7 way connector to your T350 to allow you to send the brake signal to your electric trailer brakes. To add a 7 way...
    view full answer...
  • Installing Trailer Brake Controller on 2020 Ford Transit T250
    For a brake controller for your 2020 Ford Transit T250 I would recommend the Prodigy P3 Brake Controller part # 90195. This is our best selling brake controller because of how well it works and how easy it is to setup. This is a proportional brake controller that senses the amount of braking the tow vehicle is applying and applies a proportionate amount to the trailer brakes. This will be the last brake controller you buy. It can easily be transferred to future vehicles as well. There...
    view full answer...

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