bing tracking image
  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

lowest price pledge
Our Price: $81.33
You Save: 36%
Custom Fit Vehicle Wiring

Will this fit?

To see if this custom-fit item will work for you please tell us what vehicle you'll use it with.

Orders above $99 qualify for Free Shipping
Shipping Weight: 1.82 lbs
Tekonsha Trailer Hitch Wiring - 118685
zoom in icon
slider vertical icon
zoom out icon
Comment field cannot be left empty.
Name field cannot be left empty.

Thank you! Your comment has been submitted successfully. You should be able to view your question/comment here within a few days.

Error submitting comment. Please try again momentarily.

Product Images

In Use/Installed

Customer Photos

Need help with installation?
Locate installers near me
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 118685 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 (243)
  • Q & A (0)
  • Photos
  • Why etrailer?

Tekonsha Custom Fit Vehicle Wiring

  • 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
    • Connect hot lead to battery
  • Includes ModuLite power converter 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: 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 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.

118685 Tekonsha T-1 T-Connector - 4 Wire - Modu-Lite Converter Included

Item # 118685

Installation Details 118685 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 - 118685

Average Customer Rating:  4.9 out of 5 stars   (243 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.

2021 Toyota Tacoma

I purchased a trailer hitch and a T-One Wiring Harness. I received the items that Ordered and in stalled the on my 2021 Tacoma today. The trailer hitch is of good quality, and was easy to install. The wiring harness was very easy to install, but the directions that came with it were a little vague. I viewed an installation video online that was really helpful. I am completely satisfied with my purchase, and I would highly recommend Etrailer.


Watch the install videos and you can’t go wrong. Hardest part was popping the turn signal modules out on a brand new truck. On the passenger side there are two connectors that couple to each other and not the turn signal module. Routing the power wire was easy- I cable tied it to frame members as much as possible. I didn’t need jack stands to make wiggle room as mine is a 4x4. Remember to heat the splicing connectors to shrink them down to the wires. The adhesive white patch goes on the back of the control module. Allow time for the install- maybe 2 hours- take your time. A fairly easy install even for a 70 year old.


When I first opened the package I was overwhelmed. Then I watched the install video and it became crystal clear. It took about 45 minutes to install the wiring kit.
Much better than splicing into the existing wiring harness. No worry about shorting out vehicle fuses.


Order was very quick and I installed the hitch and wiring harness in about 20 minutes

It was easy to install and works great.
-- Etrailer Expert Heather A - 10/29/2021


The instructions were right on point. The easiest trailer wiring installation I have ever done. Everything matched up perfectly…!!!


For the most part, this kit was easy to install. Since it went on a new truck, an alcohol prep pad was all I needed to use the double-face tape for the module. Removing the taillights and connecting the T-connectors was a breeze. The part that was like work was routing and securing the hot lead that runs to the battery, but maybe I'm just getting lazy. Nice kit so far.


Installing this wiring was super easy. Just be a little patient and plan your preferred wiring route. Basically a plug and play deal. The lights all worked perfect the first time. Plenty of wire length to reach all points without stretching. I think one possible improvement would be a better mount for the four-pin connector than sticky tape.. That being said, the connector is still secure. Great wiring choice!


Easy to follow instructions, very nice quality of materials, everything that was needed to do the complete job.
Good price , fast free shipping I am a very happy customer and would definitely recommend you to anyone

This is a great item no change in my review top shelf
James I - 11/14/2021


Relatively easy to install. Ample wire for my needs. Works as it should. Well worth the cost versus having it done by a shop!

Toyota Tacoma

Installed this wiring harness this afternoon. It is a good product, but I have to say that on the 2021 Tacoma I have the wire going from the right tail light to the left tail light was barely long enough. Another 6 inches would have been great. Also there are too few zip ties to safely secure the wires and keep them away from hot spots and sharp metal edges. I had to supplement the ones provided with quite a few from another project.


I want to say Thank you, shipping was delayed because the address I used, it couldn't be shipped to P.O. Box, to which I provided a physical address. I am happy with the shipping time, and I really love the product, it looks solid and durable, nothing cheap about it. The company kept me posted through the whole shipping stage, even after I received my package. I rated excellent, if you're looking for quality and great customer service I recommend I will be posting pictures this weekend, once I install it.


Excellent. I ordered this on a Thursday--I did not think it would make it in time for Father's Day. It arrived in time for the 'day'! Thank you! My husband is thrilled!


My package arrived fast, the installation was great, I am very satisfied with my products, thank you!


Works great east to hook up. Watch the video and you won't need the instructions.


It fitted perfect!

2016 Toyota Tacoma

I ordered this along with a Draw-Tite receiver hitch for a 2016 Tacoma SR 2.5L so that I could occasionally pull a small utility trailer. No factory trailer attachment options were available from the factory so this was the next best thing. Etrailer had videos out regarding the hitches and the trailer wiring options for the Tacoma before I ordered the vehicle which was very helpful. After I had the vehicle for a year or so I finally ordered the hitch and trailer wiring. The products shipped quickly and arrived promptly. The installation instructions were clear. You will need to run a 12v hot lead to your battery so it will take some time to install but it's pretty simple. The kit includes some wire ties but you will need more to do a tidy job. I also purchased some plastic wiring loom/conduit locally for better protection. I mounted the control module in a different location than what the etrailer video shows. I was able to mount it in the driver side taillight well directly behind the light assembly. It was tight but I thought the location offered better protection. After installation I decided that I didn't like the trailer wiring plug hanging under the vehicle so I found the Hopkins 41144 vehicle wiring kit fit in the bumper like from the factory. I simply bought a spare 4 prong trailer plug and with some crimp on connectors attached it to the Hopkins 4114. Now the truck looks factory and the trailer wiring is better protected.


Wiring is never a fun task but this was pretty easy and straight forward! Everything you need is included except the basic tool to do the job. You might even be able to score some extra zip ties out of the deal.

2016 Toyota Tacoma

Great product, instructions say 10 minutes but if you're like me it will take at least 30 minutes. Installing was pretty easy, what took a while was running the power wire from the battery back to the taillight. All wires/connectors/zip ties came in box.


Very easy to install. Works great. Fantastic product!


Had my hitch and wiring in two days. Everything went together perfect. Super happy with my purchase. I will definently order from etrailer again.


Great product and easy to install!


would not buy from anyone else these guys are great just try to go to a trailer hitch shop and see how you get treated then try etrailer and see the difference you order you receive very fast and you install your self or simply ask a good mechanic shop to install it if you are not familiar with wires etc and in addition etrailer will guide you thru the process over the phone or online never had a problem out of my many jeep projects nor trucks and I am only a house painter who hates assembling stuff my current hitch and huge wire assembly was installed by a tire co in 30 minutes like factory for $100 hitch shop wanted $375 and they would`nt do it unless they welded it h*ll no on a $ 60.000 truck it bolts on perfectly tx again george


Easy installation and great video

2016 Toyota Tacoma

I needed a harness for my 16 Tacoma and didn't want to splice any of the existing wiring. This fit the bill!
Everything fit perfect and if I ever wanted to remove it the stock connectors are still there. Directions were easy to follow. It came with enough zip ties to keep the wiring secured and out of the way. The plug feels solid and has fit tight with the UHaul trailers I've towed. The connector cap stays on well and as a bonus acts as a loop to keep the harness connected to the hitch.

I recommend!

2019 Toyota Tacoma

Installation wasn’t very difficult, it seems well constructed, and works great. I managed to install on a 2019 Tacoma without lifting the vehicle. The trickiest part was routing the line from tail light to battery, but the videos helped a lot. I wish I had mounted the control box a bit lower in the tail light box, as the wire between tail lights doesn’t have a lot of excess length. My first try routing that line didn’t quite reach, but I found a more direct path on the second try. Be careful to avoid any rub points against metal edges when routing wires.

Show More Reviews

Ask the Experts about this Tekonsha Custom Fit Vehicle Wiring

  • No Ground Stud Behind Tail Light to Install Trailer Wiring Harness on a 2017 Toyota Tacoma
    Since your 2017 Toyota Tacoma does not have the ground stud in question behind the driver's side tail light you would follow the alternate step in the instructions for wiring harness # 118685. And that is "Locate a suitable grounding point near the adapter such as the vehicle frame or crossmember. (Do not drill into vehicle floor or bed.) Clean dirt and rustproofing from area. Drill a 3/32” hole and secure white wire using eyelet and screw provided." Apparently some Tacomas have the stud...
    view full answer...
  • Is Trailer Wiring # 118685 for 2017 Toyota Tacoma Short Proof
    The converter of the part # 118685 that you referenced is designed to prevent trailer wiring shorts from making it to the vehicle's wiring. What will happen is the converter box will short itself out as a way prevent the short from making it to the vehicle wiring. Bad part is that it permanently damages the converter and requires it to be replaced, but at least your vehicle will be protected.
    view full answer...
  • Are the Trailer Wiring Harnesses the Same for Both a 2017 and 2018 Toyota Tacoma
    If you are referring to a trailer wiring harness then no, the trailer wiring harness for a 2017 and 2018 Toyota Tacoma will be the same. For this, I recommend using the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # 118685. This harness is a direct plug and play option that will give you a 4-way trailer connector at the rear of the vehicle without requiring you to cut or splice any wires. I have attached an install video this harness on a similar 2016 Toyota Tacoma...
    view full answer...
  • Recommended Trailer Wiring For 2020 Toyota Tacoma
    I recommend the Tekonsha T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # 118685 for the 2020 Toyota Tacoma which plugs in behind the tail lights so there is no need for a tow package on the vehicle. The black wire does need to be extended to the Tacoma's battery to power the converter. This will give you a 4-pole flat at the rear of your vehicle to power the trailer lights. The Tekonsha brand wiring has proven to be more reliable and durable than the other brands...
    view full answer...
  • Does Tekonsha Trailer Wiring Kit # 118685 Fit 2019 Toyota Tacoma 4 Cylinder
    Yes, the Tekonsha 4-way part # 118685 that you referenced does fit your 2019 Toyota Tacoma 4 cylinder as it fits all models of the Tacoma.
    view full answer...
  • Does the T-One Vehicle Wiring Harness for 2022 Toyota Tacoma Draw Power with Vehicle Off
    The T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # 118685 will not draw power from the vehicle without a trailer plugged in on a 2022 Toyota Tacoma. In other words, it won't drain the battery while the vehicle is off without trailer plugged-in.
    view full answer...
  • Recommended Trailer Wiring Harness for 2017 Toyota Tacoma
    The Plug-N-Tow (R) Short Proof Powered Taillight Converter - Heavy Duty # 46365 can be used on your 2017 Toyota Tacoma and will work fine. However, I recommend a wiring harness that makes installation easier and doesn't require splicing that also draws power from the battery to protect your vehicle's electrical components. I recommend the Tekonsha T-One # 118685. This harness plugs into your factory wiring already present behind the tail lights with quick connects and then a hot lead...
    view full answer...
  • Best Trailer Wiring Harness for a 2017 Toyota Tacoma
    Yes, we have several wiring harnesses for a 2017 Toyota Tacoma. If you are looking for a 4-way trailer wiring harness to tow a trailer then I recommend the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # 118685. If you are looking for a 7-way trailer wiring harness to tow a trailer with brakes then I recommend the Tekonsha OEM Replacement Vehicle Wiring Harness with Brake Controller Adapter part # 22117. I have also attached an install video of the 4-way harness...
    view full answer...
  • Will Trailer Wiring Harness For 2019 Toyota Tacoma Interfere With Blindspot Sensors
    There are harnesses for your 2019 Toyota Tacoma, but aren't any trailer wiring harnesses that have blindspot connections, but I can tell you that installation of a wiring harness will not interfere with any blindspot sensors. There are options to install either a 4-way or 7-way on your Tacoma and both simply plug into the tail lights and have you run a hot lead up to the battery. So the right harness will depend on if you need a 4-way or 7-way on your 2019 Tacoma: - T-One Vehicle Wiring...
    view full answer...
  • Will Taillights Work if The Vehicle Wiring Harness Convertor Module Lost Power?
    The Tekonsha T-One Vehicle Wiring Harness # 118685 will continue to send power to the vehicle taillights on your 2019 Toyota Tacoma if the power to the convertor module is lost. No power will go to the trailer taillights.
    view full answer...
  • Constant Power On Curt Harness for 2019 Toyota Tacoma
    I do have an option for you but if there is constant power on the trailer connector at any of the circuits while the vehicle is off then this indicates the converter has gone bad and the entire wiring harness will need to be replaced. The best option we have for a 2019 Toyota Tacoma is the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # 118685 which has proven to be most reliable.
    view full answer...
  • Recommended 4-Pole Trailer Wiring Harness For A 2022 Toyota Tacoma
    For your 2022 Toyota Tacoma I recommend the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118685. This 4-pole flat trailer wiring harness has custom-fit T-One connectors that plug 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. Once you've plugged in the T-connector, run the hot lead up to your car battery. Connect the lead to the...
    view full answer...
    Image 1 for
  • Trailer Hitch For A 2020 Toyota Tacoma
    The Draw-Tite Max-Frame Trailer Hitch Receiver # 75238 is the heaviest duty trailer hitch we offer for your 2020 Toyota Tacoma. This hitch has a maximum tongue weight capacity of 1,050lbs, and a maximum GTW of 7,000lbs. If you need wiring, I recommend the T-One Vehicle Wiring Harness # 118685. This wiring harness is super easy to install, and will just plug into your factory wiring harness.
    view full answer...
  • Trailer Hitch and Wiring Recommendation for 2020 Toyota Tacoma
    The Draw Tite hitch part # 75238 is a great hitch confirmed to fit your 2020 Toyota Tacoma that has plenty of towing capacity and also installs really easily. Then for trailer wiring the Tekonsha kit part # 118685 is the easiest to install and also the most reliable.
    view full answer...
  • Adding a Second 4-Way Flat Connector to Activate Brake Lighting on a Truck Cap
    I do have a solution for you, but we do not have any adapters that will plug into the Tekonsha T-One # 118252 and provide 2 female 4-Way flat connectors. Instead, I recommend installing the 4-Pole Hardwire Kit with Circuit Tester # 18252 and splice it into the T-One # 118245 right behind the female 4-Way. This kit comes with 6 feet of wire so if that is too much you will want to cut it before splicing the wiring together color for color. Please note that part # 118252 that you referenced...
    view full answer...
  • Right Turn Signal/Brake Light Stays On with Curt Trailer Wiring Harness on a 2016 Toyota Tacoma
    What you are describing sounds like a short in the converter box for Curt wiring harness # C56349 for your 2016 Toyota Tacoma. Since this is the second time this has happened it could indicate that there is something on the trailer that is causing the box to short out so I do recommend inspecting the trailer wiring and fixing any broken or pinched wires or anything else that seems problematic. I also recommend switching to the Tekonsha harness, # 118685, because we hear about less problems...
    view full answer...
  • 4-Pole Trailer Wiring Harness for 2017 Toyota Tacoma
    We do offer two choices in a plug-in T-connector 4-pole wiring harness for your 2017 Toyota Tacoma. Both are intended for trucks without the factory tow package. Please note that the term 'tow package' does not always mean the same thing. What is included in a 'tow package' can vary considerably from auto maker to auto maker, between models and even between model years. In our experience a Tacoma will either have a complete wiring set-up with wiring and trailer connector at the back of...
    view full answer...
  • Trailer Hitch Recommendation for 2017 Toyota Tacoma
    For a trailer hitch confirmed as a fit for your 2017 Toyota Tacoma you'd want to start with the Draw Tite Hitch part # 75238 which would fit and work well. It has more than enough capacity for a 2,920 lb pop camper like what you have. If you don't have trailer wiring you'll then need the T-One kit part # 118685 which is also a confirmed fit. I attached install videos for both of these for you to check out as well. If you wanted to do some towing you might be interested in etrailer ball...
    view full answer...
  • Recommended Wiring Harness For 2017 Toyota Tacoma
    Both wiring harnesses that are confirmed to fit your 2017 Toyota Tacoma require a battery line being added. This is really to protect your wiring system. The powered converter reduces strain on a factory system and protects the system. I know it seems like more work to add a power line to the battery, because it is more work, however the work will give you peace of mind knowing that your converter will function correctly and keep your factory wiring from malfunction which isn't always...
    view full answer...
  • Troubleshooting Trailer Wiring Where Brake Lights Do Not Work
    First thing you should do at this point is test the 4-way of the wiring harness with a circuit tester part # PTW2993 for voltage on all of the right pins when the taillight signals are being applied. Just like in the video I attached. If the voltage checks out there but the trailer lights still don't function right then the problem is on the trailer wiring. That would mean that problem is either due to a ground issue or a short issue. Make sure that the trailer side connector are clean...
    view full answer...
  • Trailer Wiring for 2018 Toyota Tacoma
    Good choice on the Draw-Tite hitch, part # 75238. I've linked an install video from when we put it on a 2017 Tacoma. The install is the same as your 2018. I recommend the Tekonsha wiring harness, part # 118685. It has a higher amp capacity than the Curt and they both install behind the truck's tail lights. Then you run a wire to the Tacoma's battery battery to power the converter and insert the included fuse. I've linked this install video as well on the same truck for you. If you...
    view full answer...
  • Recommended 4-way Trailer Wiring for 2017 Toyota Tacoma
    I choose the Tekonsha, part # 118685, over the Curt, part # C56349, but they're extremely similar. The only reason I choose the Tekonsha is because it has a higher amp capacity than the Curt. This can help from overloading the harness if your trailer has a lot of lights that draw a substantial amount of power. It's not a significant difference but you never know if you may need the higher capacity at some point.
    view full answer...
  • Troubleshooting Wiring Harness Connections on 2018 Toyota Tacoma
    The T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118685 is the confirmed fit for a 2018 Toyota Tacoma. The adapter on a US vehicle will give you an adapter that will reach each side correctly. There should be a connection on each side of the vehicle as shown in the attached video. You will need to make sure the connections are made on the correct side as they cannot be reversed for proper connection and function. If you do not have a US model, then you will need...
    view full answer...
  • Recommended Wiring Harness For 2020 Toyota Tacoma Towing A Trailer
    If you are just looking to tow a trailer with lights and without brakes I recommend the Tekonsha T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector part # 118685. This will give you a 4-Pole flat on the back of the Tacoma to tow a trailer with lights. The Tekonsha brand wiring has proven to be more reliable than the other brands and has the highest rated amp capacity so it can handle a little more power. It plugs into the tail light assemblies on the truck so it is a very straight...
    view full answer...
    Image 1 for Image 2 for

< Previous
123. . .4

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

  • Why

    At we guarantee:
  • Highest quality custom fit vehicle wiring for the best price.

    Our Lowest Price Pledge ensures you will never overpay for the parts you need.
  • Real product know-how.

    We make sure that the products we sell are what we say they are, and that they work the way they are supposed to work. Get real advice from a real person who has the knowledge and expertise needed to solve your problem.
  • Most detailed, accurate custom fit vehicle wiring information available.

    Because we take providing accurate product information seriously, we take our own detailed product photos, demo videos and installation videos, as well as verify measurements, instructions, and vehicle fit information.
  • Installations, made easy.

    We love helping people and have the most highly-trained customer service, hands-on experience, step by step videos and installation instructions.
  • Fast shipping.

    Your order is automatically routed to get out of our warehouse and to your door as quickly as possible. Receive free shipping on orders over $99.
  • Personalized service for life.

    We provide one-on-one, personalized service from the ordering process through the life of your product.
  • Trusted since 1946.

    We've been serving customers since our parts store first opened in 1946 and continue to be recognized by our customers, our vendors and third parties for exceptional service.
  • Returns Policy

    Need to return an item? No problem. Please read our Returns Policy for more information.

Info for this part was:

Employee Andrew K
Video by:
Andrew K
Employee Chris R
Video by:
Chris R
Employee Lindsey S
Edited by:
Lindsey S
Employee Michael H
Expert Research:
Michael H
Employee Jameson C
Expert Research:
Jameson C
Employee Jeff D
Installed by:
Jeff D
Employee Joshua S
Video Edited:
Joshua S
Employee Jacob T
Video Edited:
Jacob T
Employee Wilson B
Updated by:
Wilson B
Employee Isabelle B
Updated by:
Isabelle B
Employee Alexander C
Written by:
Alexander C
Employee David F
Test Fit:
David F
Employee Bradley B
Test Fit:
Bradley B

At we provide the best information available about the products we sell. We take the quality of our information seriously so that you can get the right part the first time. Let us know if anything is missing or if you have any questions.