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Tow Ready Tail Light Isolating Diode System with 4-Pole Connector

Tow Ready Tail Light Isolating Diode System with 4-Pole Connector

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This combined diode system features a Y-harness that allows your RV to power the lights on your towed vehicle without the vehicle sending electrical feedback to the RV. The 2-diode system does the work of 4 and protects both electrical systems. Lowest Prices for the best tow bar wiring from Tow Ready. Tow Ready Tail Light Isolating Diode System with 4-Pole Connector part number TR118821 can be ordered online at or call 1-800-940-8924 for expert service.
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Tow Ready Tow Bar Wiring

  • Diode Kit
  • Splices into Vehicle Wiring
  • Universal
  • Tail Light Mount
  • Tow Ready

This combined diode system features a Y-harness that allows your RV to power the lights on your towed vehicle without the vehicle sending electrical feedback to the RV. The 2-diode system does the work of 4 and protects both electrical systems.


  • Kit includes everything required to wire vehicles with a 2-wire system for towing behind a motor home
    • Y-Harness with 1 driver's-side and 1 passenger's-side diode
      • Each diode contains a tail light and combined turn and stop feed
    • 4-Pole flat connector extension
      • Runs along your tow bar
      • Connects RV wiring system to the Y-harness
    • 8 Wire connectors, 1 ring terminal and 4 zip-ties
  • System connects your RV turn signals, running lights and brake lights to your towed vehicle's lights
  • Mounting bracket for 4-way flat connector (18144) sold separately
  • 1-Year limited warranty

Tow Ready Tail Light Isolating Diode 2 wire to 2 wire diagram

Tow Ready Tail Light Isolating Diode 2 wire to 3 wire diagram

Please note for 3-wire system on towed vehicle: With this kit, the towed vehicle's brake lights will function as both the brake and turn lights. A wiring converter (118158; sold separately) and 2 additional diodes (also sold separately) will be needed if you want to retain separate turn and brake signals.

118821 Tow Ready Tail Light Isolating Diode System with 4-Pole Connector

Item # TR118821

Installation Details TR118821 Installation instructions

This Product Fits The Following Vehicles

California residents: click here

Customer Reviews

Tow Ready Tail Light Isolating Diode System with 4-Pole Connector - TR118821

Average Customer Rating:  4.8 out of 5 stars   (177 Customer Reviews)

This combined diode system features a Y-harness that allows your RV to power the lights on your towed vehicle without the vehicle sending electrical feedback to the RV. The 2-diode system does the work of 4 and protects both electrical systems.


Instructions were helpful, I ran the wire through the inside of my Mini Cooper. Real easy, did not needed to lift the car. Works well


I have yet to install the wiring harness but will do so in the next few weeks in preparation for a trip this summer. Inquire again next year and I will respond.

I installed and used the wiring harness last year from Florida to Massachusetts and back. It was easy to install and worked perfectly the whole trip.
Norman - 03/14/2022

1997 Suzuki Sidekick

The tow ready tail light isolating diode system is what i need but the installation instructions does not apply to my vehicle. I have a 1997 Suzuki sidekick JX. The instructions says, remove the cover to compartment where jack is stored, to access the wiring harness and find plug. My jack is stored under the passenger front seat. No storage compartment in rear of vehicle. So far i haven't found the harness I'm suppose to unplug more later when and if i find it.


I’m giving it 5 stars only for the fact that it works as described but instructions lack on its installation I had to go online and lookup the manufacturer on how to hook it up on tail lights..

Sorry for the installation trouble. Here is an installation video for a 2019 Jeep Cherokee:
-- Etrailer Expert Sierra K - 12/22/2021


Needed help from etrailer's tech support, as color code was different.
Tech support was great. Item works as intended!

Have towed thousands of miles with no problems!
Chuck - 01/27/2022


Was able to travel a lot of states with the hook up, all worked as expected and I appreciate all the help Roger gave me. Will definitely purchase from etrailer in the future.


This has worked perfectly. It was easy to install and is still working great after a year of use.

Wonderful! Still working perfectly.
Brittainy - 06/02/2022

2019 Ram 1500

Have not installed the wire
ing kit as
of yet

2019 Dodge Ram Pickup

I am very pleased with the Demco setup. I'm towing my 2019 Ram 1500 behind 2017 Tiffin Phaeton bus. With the help of etrailer videos I was able to install the base plates, light wiring, brake system and battery charger completely by myself. It took some effort and a couple of days but save lots of money and know that it is done right.


I replaced a previous version and found this one was easier to installed.


easy to install I am very happy with your product, the video you provided was a great help, I just moved the brake indicator LED to the Motorhome dash instead of the tow vehicle and I provided power to the controller from the motorhome.


Knowledgeable staff on what will work and what you should avoid . The Videos are super helpful and very informative and they tell you what would be the better product not just sell you the most expensive products.

This wiring was easy to make all the connections. The hardest part was getting the wiring from the back lights through the frame and body up to the front connection. Once that was completed the remainder went pretty quickly.
Dave E - 05/12/2021


Easy install and works flawless. Our second time using this product with great results.

Still working with no issues
Jack - 12/28/2021


Great company to deal with. Very helpful people who know answers to your needs.


Easy install. Works great after 1 year


I used this product with Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector
Item # C56407 in order to prevent splicing into the vehicle wiring harness. It was more expensive but it created a plug and play solution for my gladiator Jeep. Follow the videos to a t and you cannot go wrong also follow the attached diagram if you are going use my trick or wire by splice. It will save you some trouble shooting time.


Installing this kit was no small feat. It required disassembly of the rear bumper and taillight assemblies, as well as snaking the wiring - intelligently - all the way from the back to the front. However, once installed it's been performing admirably for over a year and 10k miles of towing.


Sent parts wrong location ????

Thank you for letting us know! We will have our customer service team reach out to you.
-- Etrailer Expert Brooke M - 08/30/2021


As advertised. Installed on 2020 Ford Ranger. The biggest problem is running the wire from the back of the truck to the front. Removing the spare tire makes installation much easier.


Followed directions and completed job in a little over 4 hours. had trouble reinserting some pins in difficult locations.

Later in the month I installed the wiring tow package. Goofed up and crossed a wire and it took me two days to get back under the truck and rewire. all is working great according to directions...…….

I will use etrailer again, good service, great service representatives...……..jt


Working great. No issues


Worked perfect for my 2021 Jeep Gladiat or.


I still have not spliced into Jeep. The wires came up short going across the rear tail lights, even after ensuring there wasn't any wires not snugged up.


2019 GMC Canyon

Installed in my 2019 GMC Canyon. Works well with no issues. We like using our factory running lights and turn signals. A good add, we are happy.

2018 Jeep Wrangler

Excellent lighting kit for flat towing another vehicle, worked great and easy install on my 2018 Jeep Wrangler JL

Show More Reviews

Ask the Experts about this Tow Ready Tow Bar Wiring

  • How Difficult is it to Install the Tow Ready Tail Light Isolating Diode System # TR118821
    As long as you are used to doing your own work on your vehicle, most of the lighting systems that we have are fairly easy installs. The Tow Ready Tail Light Isolating Diode System # TR118821 will install on your 2017 Chevrolet Spark by splicing the current wiring which send the left brake and left turn, right brake and right turn, and tail lights into the diodes on the Tow Ready System. See attached photo for for illustration.
    view full answer...
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  • Install Instructions for Tow Ready Tail Light Isolating Diode System TR118821
    I attached the two sheets of the install instructions for the Tow Ready Kit part # TR118821 that you referenced.
    view full answer...
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  • Troubleshooting Tow Ready Tail Light Isolating Diode System TR118821
    If you have your input and output connections correct on the Tow Ready Tail Light Isolating Diode System # TR118821 and it still does not function I suggest checking the white ground wire with ring terminal is affixed to a clean bare metal point to ensure a good connection. Even if all the other clip on connectors are properly installed without a strong ground the harness won't function. You can try sanding off the grounding point to expose clean bare metal and reattaching the ground ring...
    view full answer...
  • Will Tow Ready Tow Bar Lighting Kit # TR118821 Fit 2018 Jeep Wrangler JL Unlimited
    Yes, the Tow Ready Tow Bar Lighting kit part # TR118821 that you referenced would work great on your 2018 Jeep Wrangler Unlimited. It is perfectly compatible with LED taillights as well.
    view full answer...
  • How Long are the 4-Way Wiring Harnesses of Tow Ready Flat Tow Diode Kit # TR118821
    There are two sections of 4-way wiring on the Tow Ready Tail Light Isolating Diode System with 4-Pole Connector # TR118821 that you referenced. There's a section that attaches to the converter boxes which measures 60 inches and there's a 25 feet long section that spans from the front of the towed vehicle to the wiring at the rear of the tow vehicle.
    view full answer...
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  • Will Tow Ready Diode System # TR118821 Work On 1998 Geo Tracker
    Yes, the Tow Ready Tail Light Diode System # TR118821 referenced in your question will work great on your 1998 Chevy Geo Tracker. This is a combined diode system that will let you tap into the signal light circuits on your Tracker so they will accept those from the RV while being towed. It includes a 4-Way connector and extender loop to connect with a 4-Way on the RV. I have attached a short video review along with the written installation manual that you can check out as well. In order...
    view full answer...
  • Does Tow Ready Tail Light Isolating Diode System with # TR118821 Fit 2010 Hyundai Elantra Touring
    The wording of our fitguide is a bit confusing but the Tow Ready Tail Light Isolating Diode System with 4-Pole Connector # TR118821 that you referenced does fit your 2010 Hyundai Elantra Touring model. It's listed in both places of the fitguide as a fit for the touring models and a fit for non-touring models so depending on where you see it as you are scrolling it's easy to be confused.
    view full answer...
  • Wiring Tow Ready Tail Light System for 2017 Ram 3500 With Combined Wiring
    Your 2017 Ram 3500 is a 2-wire combined system which means a wire for the turn and brake, and another for the tail light. So when when wiring the Tow Ready Tail Light Isolating Diode System with 4-Pole Connector # TR118821 you need to do so like in the following diagram. I have also added a link to the instructions and a video install.
    view full answer...
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  • Troubleshooting Wiring Issue on 2000 Jeep Cherokee Using Wiring Harness 118821
    The Tow Ready Tail Light Isolating Diode System with 4-Pole Connector # TR118821 are a fit for your 2000 Jeep Cherokee. Often when there is a wiring issue like this on the vehicle side, it is due to a bad ground connection. I recommend checking your ground wire connection to make sure it is bare metal to metal and free of corrosion or debris. I recommend using a little sand paper at that connection and then reconnecting to see if it solves your issue.
    view full answer...
  • Troubleshooting Running Lights of Vehicle Not Working of Tow Bar Wiring Install
    Sounds like the issue is where you tapped into the running light circuit of your 2019 Jeep Cherokee. If the running lights still work when using the tow bar wiring but not during normal driving of the vehicle that would indicate that where you tapped into the circuit is not connected properly so you'd want to go over the connections there to see what's not connected properly. Also make sure you didn't blow the running light fuse of the vehicle in the fuse box.
    view full answer...
  • Troubleshooting Tow Ready Wiring for Flat Towing a 2009 Chevy HHR
    If everything is working just fine on your 2009 Chevy HHR when you aren't towing then the problem is either on your motorhome wiring or on the wiring between the diode for the # TR118821 and the 4-Way that connects to your motorhome. You can test this by applying 12V power to the different pins on the 4-Way to see if everything works correctly on your vehicle without being connected to the motorhome. If it does then you know that this whole wiring kit is okay and you need to check the...
    view full answer...
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  • Troubleshooting Tow Bar Wiring Install Brake Lights Come On When Vehicle is In Reverse
    If what you installed was the part # TR118821 that you referenced you should note that this kit was not designed for attaching to the reverse light circuit at all. The fact your brake lights come one when putting the vehicle in reverse would indicate you ran the stoplight circuits of the kit to the reverse lights instead of the brake lights.
    view full answer...
  • Compatibility of TR118821 Taillight Isolating Diode System w/ OEM LED Taillights on 2014 Ram 1500
    A diode based system like the Tow Ready # TR118821 doesn't care if the taillights are LED or incandescent, so it'll work just fine on your 2014 Ram 1500 with the OEM LED taillights. If you click the provided link, you can see the # TR118821 being installed on a Ram 1500. You'll also need a tow bar, base plates, safety cables, a supplemental braking system and possibly a high/low adapter. If you'd like some suggestions for those items let me know and I'd be happy to help.
    view full answer...
  • Troubleshooting Tow Ready Tail Light Isolating Diode System for 2018 Jeep JK Wrangler Unlimited
    It sounds like you have a bad/failed connection on your installation of the Tow Ready Tail Light Isolating Diode System with 4-Pole Connector, # TR118821. I suggest that you first check the ground connection and ensure that it is made to a clean bare metal surface that is free of corrosion and verify all connector pins are properly seated and not damaged. Then work back from one end of circuit to the other performing a continuity check and looking for any damaged wires.
    view full answer...
  • Locating Correct Wires on 2019 Jeep Cherokee to Install Tow Ready Tail Light System # TR118821
    The best method for locating the correct wires to splice into on your 2019 Jeep Cherokee when installing the Tow Ready Tail Light Diode System # TR118821 is to simply test them using a circuit tester like # 40376. Going by wire color alone isn't always a good idea as vehicle manufacturers tend to switch up the wire colors used at the factory. What you will want to do is remove the tail lights so you can access the wiring. Then you can have a buddy run through the lighting functions in the...
    view full answer...
  • 2020 Jeep Gladiator Taillight Wiring Harness Wire Colors for Installing Flat Towing Diode Harness
    I can certainly help with that. When we installed a similar system on a 2020 Jeep Gladiator, we found that in the drivers side taillight harness, the yellow wire carries the left turn/left brake lamp circuit, so that's where to attach the yellow wire. The white wire with the gray stripe carries the left side running lamp, which would attach to the brown wire. On the passenger side taillight harness, the green wire carries the right turn/right brake lamp circuit and the white and orange...
    view full answer...
  • Will The Tow Ready Flat Tow Wiring TR118821 Fit A 2021 Jeep Gladiator?
    I will start by saying that the Tow Ready Tail Light Isolating Diode System with 4-Pole Connector # TR118821 will definitely work with your 2021 Jeep Gladiator. I included an install video we did on a Ram that will be very similar to how you will be doing it, but you will need to test your wires with something like the # 40376 circuit tester to make sure you are tapping into the correct functions. This kind of wiring is more involved than trailer wiring, so just take your time. I included...
    view full answer...
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  • Tow Bar Lighting Recommendation for 2017 Ford Focus
    It's a somewhat common misconception that vehicles with separate taillight circuits have to be wired for separate tow bar wiring. You actually can wire just the brake lights of the vehicle to operate as a combined circuit and it will be much simpler to do, and will be just as effective. So the kit part # RM-15267 would come with everything you'd need and wouldn't require any additional adapters. We actually had the chance to install this on a similar 2012 Ford Focus and it worked really...
    view full answer...
  • Wiring Kit for Flat Towing to Allow for Quick Connection of Toad and RV
    If your towed vehicle has a 4-pole connector for its wheels-down lighting kit you can install a socket to avoid having the wire hanging down when you're not towing it. Blue Ox kit # BX8861 includes two 4-pole round sockets (one for the car and one for the RV) as well as a coiled 4-pole cord. What you can do is cut off the 4-pole connector on the car wiring and connect it to one of the sockets that will mount on the car bumper cover. The other socket will install on the RV and splice into...
    view full answer...
  • Wiring Kit Needed to Activate 2012 Kia Sportage Lights While it is Dolly Towed
    We sure do have some kits that you can install on your 2012 Kia Sportage to activate the lights when you are towing it with a tow dolly! If your tow vehicle has a 7-Way then I recommend installing the Flexo-Coil Wiring Kit # RM-15267. If you have a 4-Way on your tow vehicle then I recommend using the Tow Ready Tail Light Isolating Diode System # TR118821 instead. Both wiring systems tie into the lighting on your Sportage and protect the wiring on your tow vehicle via diodes. I have linked...
    view full answer...
  • Trailer Wiring Recommendation for 1973 Volkswagen Thing
    We don't have trailer wiring that's confirmed as a fit for your 1973 Volkswagen Thing, but normally the circuit you'd need to tap into for the running light circuit of trailer wiring is the taillight circuit that comes on when the headlights of the vehicle are on. I looked up the taillight configuration of your vehicle though and it looks like there is a separate amber bulb for the blinkers from the brake lights. So what you'd need is a wiring harness with a converter box so that you can...
    view full answer...
  • Diode Kit Tow Bar Wiring/Lighting Kit Recommendation for 2019 RAM 1500
    Yes, we have confirmed that the Tow Ready Tail Light Isolating Diode System with 4-Pole Connector # TR118821 that you referenced is a fit for your 2019 Ram 1500 with LED taillights. I attached an install video that shows a similar diode tow bar wiring kit part # RM-15267 installed on a 2019 Ram 1500 just like yours to use as a guide for the install as well. You might prefer this kit too as it comes with an umbilical cord to go from the tow vehicle to the towed.
    view full answer...
  • Can 4-Way Flat Extension be Used to Connect Trailer Wiring on 2000 Jeep Wrangler to RV 4-Way Flat
    I believe you are referring to the 4-Way Flat connector on your 2000 Jeep Wrangler that is used for towing a trailer. If this is the case then an extension won't work as the current wiring on your Wrangler is designed to send power and not receive it. Instead what you need is a tow bar wiring kit that is designed to receive power and activate the lights on your Wrangler. For your application I recommend the Tow Ready Tail Light Isolating Diode System # TR118821 because it comes with the...
    view full answer...

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Notes: Item is missing the wire connectors. Otherwise new and unused.

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