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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 # 118509
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118509 - 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. 1-800-940-8924 to order Tekonsha custom fit vehicle wiring part number 118509 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 (47)
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  • Why etrailer?

Tekonsha Custom Fit Vehicle Wiring - 118509

  • Custom Fit
  • Trailer Hitch Wiring
  • 4 Flat
  • Powered Converter
  • Tekonsha

Quickly and easily install a 4-way trailer connector on your vehicle with this custom wiring harness. T-One connector plugs directly into existing wiring. Powered ModuLite reduces strain on wiring system.


  • Provides a 4-way flat trailer connector at the back of your vehicle to power your trailer's signal lights
    • Compatible with 5-pole, 6-pole and 7-pole adapters (sold separately)
  • Connects quickly and easily
    • Locate connection points in rear cargo area
    • Plug in T-connector
    • Run hot lead to car battery
  • Includes ModuLite to ensure that your vehicle's wiring matches that of your trailer
    • Powered module connects directly to battery to avoid overloading vehicle's electrical system
  • Constructed of 16-gauge bonded wire
  • Comes with dust cap for 4-way flat connector


  • Maximum amperage:
    • Stop/turn lights: 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 interior trim panels in your rear cargo area. 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 within the jack storage compartment of 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.

118509 Tow Ready T-1 T-Connector - 4 Wire - Modu-Lite

Installation Details 118509 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 - 118509

Average Customer Rating:  4.8 out of 5 stars   (47 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.


Installed the kit on my T2 2008 Touareg for towing a [car transporter] (Has surge brakes to supplement trailer brake kit on your Touareg) from California to the East Coast. Installation video and instruction are very accurate and helpful. The kit is well made. Would recommend it any day if you don’t have a factory trailer wiring. Had it for 1 year without any issues.

Works great after two years of use on a T2 VW Touareg
Touareg T - 05/25/2021

2010 Volkswagen Touareg

After reading all the reviews and how to videos I decided to order the T-One wiring harness. I've cut, spliced and fabricated many a trailer wiring harness on numerous vehicles. Installing this was like sleeping in on a Sunday morning. Easy. Relaxing. Simple. Enjoyable. Wow!!!!
I had just installed the Curt Trailer hitch, button up my rear bumper and started on the wiring. Watch the videos by etrailer!!! Great job. ETrailer alway has what I need!!

Aside from having to completely rerouting the power wire because it got tangled in my steering linkage everything works as it intended. Still towing trailers and all the lights and connections still work.
Stephen - 05/27/2017

2004 Volkswagen Touareg

I thought this kit was amazing, a truly plug-and-go solution. The video that etrailer has was fantastic and made the install very straightforward. I had never done a job like this (I've installed stereos, done basic automotive repairs) and this took me about 35 minutes (I was installing a hitch at the same time). Very happy with the kit. Oh - little tip for you - my 2004 VW Touareg has a couple 12V cigarette lighter outlets in the back cargo area - use those for power! Forget running power up to the battery or underneath the truck - use those as they make for a clean and quick install. I just plug in when I need to tow, and unplug and stow the wires when I am not. Great time saver!

We do recommend for the power wire to be wired directly to the battery to avoid overloading the circuit and damaging your vehicles wiring. The 12 volt accessory circuit was not designed to support the additional load of a trailer wiring harness. I have attached an article about routing the power wire.
-- Etrailer Expert Heather A - 06/09/2018


Extremely easy to install and worked pe rfect.

2005 Volkswagen Touareg

I installed a hitch and harness on a 2005 VW Touareg. This was rated by eTrailer 10/10 for difficulty.
I am 74 years old, with no technical training, but I have worked on cars most of my life. Installing the hitch was straight forward, though I would not want to have done it without the excellent video provided by etrailer. Reassembly was a bit of a pain, because some of the valance attachments in the rear wheel wells had rotted. The harness was more complicated, though, again, the video was extremely helpful. etrailer recommended running the hot wire outside the vehicle to the engine compartment. I didn't like this idea, and decided to run it through the interior, to the battery, which sits under the driver's seat. This involved lifting a lot of trim and carpet, and removing the driver's seat, all of which was tiresome work. However, on completion, everything worked. The whole project took nearly six hours - two for the hitch, and almost four for the harness. I would recommend this product and the indispensable installation videos.

2008 Volkswagen Touareg

What an easy installation. I reviewed the youtube video before the hitch arrived and started it when i got home. The which went on in about 40 minutes and the wiring, although, i watch a couple of videos of other years wiring harness installation i chose to go with the one best suited for my installation. Pretty much went without a problem....


Product arrived in a timely manner, great price point. This is the third hitch and wiring kit I have purchased form The help videos made it clear how to install hitch and wiring kits. I am a very satisfied customer and will returning here for the next one.

2006 Volkswagen Touareg

Plug and play product; OEM quality. Can't imagine having the job go any smoother than it did; the hardest part of the job was running the hot wire to the battery so that it was totally concealed and protected under the car. Take your time and don't be afraid to unbolt a few covers and guards under the car to tuck the wire in for protection but don't pinch it!

Experience doesnt get any better than the one I had with etrailer! Keep up the good work.
Phil S - 08/17/2015

2004 Volkswagen Touareg

Was pretty straight forward. The only thing I did different was wired in a 7 pin connector perminately. I did not like that the wire just hangs out of the tail gate.

Still working great, no issues! Ill use you guys again for my next purchase.
Chris R - 11/01/2017

2006 Volkswagen Touareg

I purchased a receiver hitch and a plug n play wiring harness for my 2006 VW touareg. My order arrived on time and in great shape! This product is heavy duty and durable! The customer service from the company has been great as well! Thank you very much, I will definitely recommend this product to others!

2009 Volkswagen Toureg

I have installed the wiring harness on my 2009 Volkswagen Toureg and found it to be relatively easy. Everything fit as advertised. The only problem was accessing the battery, which was no fault of the harness.

2008 Volkswagen Touareg

High quality product with great video. Install was straight forward. Will keep coming back to etrailer!


Excellent product! Many resources for help with installation.


A lot of good things to say. Fast order process and shipping. Helpful sale people. As advertised easy installation. Hardest part was running power wire from cargo area to engine compartment. That bad I give to VW. Instuctions were easy to understand, but lacked a few details. Would like to see control module on passenger side (plug in conectors) instead of driver side (storage compartment). Kit included everything you need for the install. Works great. Thanks


I have never installed a aftermarket hitch and wiring harness. I always installed factory parts. I tried harness and hitch from e trailer and I am sold. They had fast delivery and everything was great!!

2007 Volkswagen Touareg

The wiring harness was a perfect plug and play installation. Didn't have to splice/tap a single wire. The instructions left a lot to be desired but nothing you can't work around. Would definitely buy again.

2008 Volkswagen Touareg

I've purchased hitch and wiring for 2 different vehicles and I couldn't be happier. Great products, easy enough instructions for install and connections and no problems. Thank you etrailer!

2004 Volkswagen Touareg

Works great, very easy to install. Great resources on the sellers website to assist with the install. My only criticism would be that the part that plugs into the tail light could be a little longer. The original wiring comes out about 6 inches which makes it really easy to remove the tail light. However with this installed, you can barley get your hand in to un-clip it.

2004 Volkswagen Touareg

Super quick shipping! Installed by myself and it went pretty quickly. I was nervous as this was installed on an '04 VW Touareg and I had read that aftermarket harnesses would cause error icons on the dash due to electrical monitoring that the VW uses. With this harness it has a separate power supply so it does not effect the cars on board electrical monitoring. Works perfectly!


Installation and operation easy

2005 Volkswagen Touareg

I have always found Tekonsha products to be first class. Works great.

2010 Volkswagen Touareg

Wiring harness went in like a breeze no problems at all. We did watch the video first.

2008 Volkswagen Touareg

The wiring kit should have been designed to mount on the passenger side of the vehicle. The storage area has power (Connector for the OEM module location), ground stud near tail light, and enough room.

2009 Volkswagen Touareg

Easy enough to complete following the video. I absolutely HATED reinstalling the tail lights. The new connector was extremely short. That is the only reason I gave the 3/5 star rating.

2008 Volkswagen Touareg

the best tracking order system i have ever seen, product was perfect, installing was a dream, thank you etrailer!

Show More Reviews

Ask the Experts about this Tekonsha Custom Fit Vehicle Wiring

  • Trailer Wiring Harness Shows No Power After Installation on a 2007 Volkswagen Touareg
    Trailer wiring harness # 118509 is a powered converter that requires a direct connection to the vehicle battery. If you did not make the connection to the battery or the fuse is missing or blown then it would not show any power on any of the circuits (when activated). If the connection to the battery is good and the fuse is inserted then check the ground connections (white wire). It must be attached to a clean and corrosion free bare metal surface. No paint or anything. And it works best...
    view full answer...
  • Does Wiring Harness 118509 Fit 2008 VW Touareg Without Factory Trailer Connector?
    Yes, I can confirm for you that the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118509 is a fit for a 2008 VW Touareg without a towing package. This harness will give you a 4-flat connector for use at the back of your vehicle. I have added links to a video review and install, as well as the instructions for you to take a look at.
    view full answer...
  • Can 4-Flat Harness for 2010 VW Touareg be Bought Without Module?
    The T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118509 that fits your 2010 VW Touareg cannot be purchased without the powered module; it is a part of the kit and comes included.
    view full answer...
  • Customer Feedback and Installation Tips for the Tow Ready Wiring Harness on 2004 Volkswagen Taureg
    Thank you for the feedback on the install of the Tow Ready Wiring harness part # 118509.
    view full answer...
  • Is Splicing and a Battery Connection Required to Install Trailer Wiring Harness on 2006 VW Touareg
    The wiring harness, # 118509, for the 2006 Volkswagen Touareg just plugs in line with the vehicle tail light wiring. You do not have to splice into the vehicle wiring for installation. You will need to connect the harness to the vehicle battery. The battery connect actually powers the trailer lights while the connection to the tail light wiring provides the signals, not the actual power for the lights. I have included a link to the installation instructions and a link to an FAQ with tips...
    view full answer...
  • Can Cigarette Lighter be Used to Power T-One Vehicle Wiring Harness on 2004 VW Touareg?
    You should not use the cigarette lighter to power the T-One Vehicle Wiring Harness # 118509 on your 2004 VW Touareg, you need to run a hot lead directly to your vehicle's battery. This harness has a ModuLite which needs to connect to your VW's battery and is designed to prevent overloading your vehicle's electrical system, which would be vulnerable if you keep your vehicle wired as is.
    view full answer...
  • Troubleshooting Trailer Lighting That Stops Working When Running Lights Come On
    Your main problem is an insufficient ground for the trailer wiring. Try improving the connection of the main ground wire of the trailer wiring harness. Make sure it is attached to a clean metal surface. Or you can run all of the trailer wires back to the main ground. This is actually the ideal solution. But you can also check the current grounds for the lights to make sure they are making a solid connection to a clean metal surface. What you described is the classic insufficient ground...
    view full answer...
  • Does T-One Vehicle Wiring Harness 118509 Need Power Wire Run Directly To Vehicle Battery?
    The Tekonsha T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118509 you were looking at for your 2008 Volkswagen Touareg needs to be run directly to the vehicle battery as shown in the included video and installing it in a different matter can void the warranty of the harness. The reason for this is connecting it to an existing circuit like the 12v outlets mentioned can overload that circuit and cause you to blow that fuse making you lose trailer lights, or worse, damage...
    view full answer...
  • Hitch, Wiring and Related Items to Tow Utility Trailer with 2004 Volkswagen Touareg
    Different versions of a given vehicle can have varying towing capacities based on their engine, transmission and suspension packages, so it is best to check your own VW owner's manual to see what the car's rated towing capacity is. I reviewed online resources that indicate some versions can tow as much as 7700-lbs. A check of your manual is in order. Since your car can be fitted with a 2-inch Class III hitch chances are good that it will have a pretty good rated towing capacity. The hitch...
    view full answer...
  • How to Install a Brake Controller in a 2007 Volkswagen Touareg with a Factory 7-Way
    To install a brake controller in your 2007 Volkswagen Touareg you will need to get some parts from your local Volkswagen dealer. I wish we carried the needed part but we do not. For more information check out the tech bulletin I attached. The brake controller we recommend the most is the Prodigy P2 Brake Controller part # 90885. This is the best selling controller on the market because of how easy it is to setup and use, and how well it works.
    view full answer...
  • Trailer Wiring Recommendation for 2011 Volkswagen Tiguan
    For your 2011 Volkswagen Tiguan we only have universal fit trailer wiring fits like the part # 119190KIT which I attached an install video for on a similar Tiguan as yours. The # 118509 does not fit your vehicle so I cannot recommend it.
    view full answer...
  • Trailer Signal Lights Malfunctioning After Installing Optronics Tail Light
    From what I can see in your question, it seems like the most likely cause for the signal lights on your trailer to be malfunctioning after installing the Optronics Sealed Stop, Turn and Tail Light # STL78RB is the ground connection on your trailer. You mentioned grounding the white wire from the new light to the metal body of the door hinges. I strongly recommend finding a more suitable ground on the main trailer frame for this wire. A weak or bad ground can certainly lead to many different...
    view full answer...
  • Trailer Wiring Kits for 2009 Volkswagen Touareg TDI
    The Curt 7-Way Wiring Adapter # C57003 is a special type of adapter that is used when certain import vehicles like VWs tow a trailer that has LED type lighting. LED lights use very little power so they can sometimes have compatibility issue with vehicle wiring that is expecting to see the much higher power draw from standard incandescent-type bulbs. This adapter does plug into a 7-way and in turn provides a new 7-way socket for a trailer's plug. This connector format carries lighting, trailer...
    view full answer...
  • Trailer Wiring Harness For 2005 VW Touareg
    You won't need to hard wire your Touareg, there's a plug and play option available as part # 118509. You can see an install video by using the link I provided.
    view full answer...
  • Complete Trailer Wiring and Brake Controller Recommendations for a 2004 Volkswagen Touareg
    Yes, this Tow Ready Custom Fit Vehicle Wiring, part # 118509, is the correct trailer wiring harness for your 2004 Volkswagen Touareg. I attached installation instructions for this product for you to check out. Having a brake controller when pulling a trailer is never a bad idea. I would recommend the Tekonsha Prodigy P2 Brake Controller, part # 90885, as it is our best seller because of how easy it is to use and how well it works. Instructions are attached. Next thing you will need to...
    view full answer...
  • Towing Hitch Recommendation for 2004 Volkswagen Touareg
    If you have a 2004 Volkswagen Touareg then we do have hitch fits for your vehicle like what you mentioned, but we don't have anything for a 2002 model as that isn't a year they had a Touareg to our knowledge. The hitch I'd recommend is the Curt part # 13220 though as its advantage is that it is made in the USA and has the better price currently. All other things are basically equal though as far as weight capacities and install time. For trailer wiring then the best option is the very...
    view full answer...
  • Converting Wiring On 2008 Volkswagen Touareg To Tow Trailer With 3-Wire Lighting
    Unfortunately we do not sell the modulate unit or the harness by itself. We receive these as a complete unit and individual parts are not made available to us. I do have a solution for you. You can use the # 118509 kit on your Touareg. This will give you a 4-way trailer connector. You can attach part # C56196 to convert the signal back to a 3-wire on the trailer. You will need to attach a 4-way to the converter for the trailer. I recommend part # HM48205. This includes both a trailer...
    view full answer...
  • Trailer Hitch and Brake Controller Recommendation for 2004 Volkswagen Touareg
    If your 2004 Volkswagen Touareg came with a factory 7-way trailer connector, then the additional brake control harness that you will need must be obtained from a Volkswagen dealer. Unfortunately aftermarket brake controller manufacturers do not offer this harness. The harness will plug into a mating connector underneath the drivers side dash and splice to the wires coming from the brake controller. If your vehicle does not come with any trailer wiring you would need to first need to start...
    view full answer...
  • Recommended Trailer Wiring Harness for 2011 VW Tiguan
    For your 2011 VW Tiguan there is not currently a T-connector harness available. You can use either the Upgraded Heavy Duty ModuLite Circuit Protected Vehicle Wiring Harness with Install Kit # 119190KIT which uses the quick connect splice connectors or the ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit # 119250KIT which connects without splicing into your factory wiring. Either option will work well for your Tiguan to give you a 4-way...
    view full answer...
  • Parts Needed for Brake Controller Installation in 2004 Volkswagen Touareg
    If your 2004 Volkswagen Touareg does not have a factory trailer connector at the rear then brake controller installation will require you to first install a 4-pole flat wiring harness like # 118509 and then to use our brake controller install kit # ETBC7 which contains all parts you'll need except for the controller itself. You can then install a controller like the highly-rated Prodigy P2 # 90885 or the P3 # 90195. If you have a factory 7-way trailer connector I recommend the Curt Echo...
    view full answer...
  • Availability of a Plug and Play Wiring Harness for a 2006 VW Touareg.
    We do offer a plug and play trailer wiring harness for the 2006 VW Touareg, part # 118509 which plugs inline between the taillight wiring harnesses and the taillight assemblies. You'll need to run a power feed to the vehicle's positive battery terminal to provide a power source that's isolated form the vehicle's wiring system. I've linked to an install video that you'll find helpful.
    view full answer...
  • Trailer Wiring Harness Recommendations for a 2005 Volkswagen Touareg
    Tow Ready wiring harness # 119190KIT is not one of the recommended trailer wiring harnesses for your 2005 Volkswagen Touareg. I have included a link to the harnesses recommended for your vehicle. Two of them are hardwire harnesses but there is also a T-one style connector that plugs in line with the vehicle tail light wiring, # 118509. If you wanted to go with a hardwire type of harness then you could use # 119147KIT. We have not yet installed this harness on a 2005 Touareg so we do not...
    view full answer...
  • Brake Controller Recommendation for 2004 VolksWagen Tourareg Towing 3200-lb Travel Trailer
    Among the easiest to set-up brake controllers is the popular and reliable Tekonsha Prodigy P2, part # 90885. This unit is highly rated by our customers for its simple operation. This is a proportional-type controller that costs a bit more than the time-delayed units but will save wear and tear on your Touareg's brakes. The linked article explains the merits of each type of controller. Along with your brake controller you will need an installation kit, part # ETBC7. This kit includes the...
    view full answer...
  • Installation of a Tow Ready Harness # 118509 On a 2004 Volkswagen Touareg
    I attached installation instructions for this T-One Connector w/Upgraded Circuit Protected ModuLite, part # 118509, below for you to check out. You will not need to remove the rear bumper for this install. Basically, you will remove the tail lights temporarily so you can access the the wiring harness for each of the tail lights and then you will wire this harness in line with the tail light harness and then you will ground a wire to the body of your 2004 Volkswagen Touareg and finally...
    view full answer...

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