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Vehicle to Vehicle Tail Light Converter

Vehicle to Vehicle Tail Light Converter

Item # 118158
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Tow Ready Tow Bar Wiring - 118158
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Used when a motorhome with a 2-wire system is towing another vehicle with a 3-wire system, by way of a tow bar. Lowest Prices for the best tow bar wiring from Tow Ready. Vehicle to Vehicle Tail Light Converter part number 118158 can be ordered online at or call 1-833-496-1390 for expert service.
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Tow Ready Tow Bar Wiring - 118158

  • Tail Light Converter
  • Splices into Vehicle Wiring
  • Universal
  • Tow Ready

Used when a motorhome with a 2-wire system is towing another vehicle with a 3-wire system, by way of a tow bar.


  • Used when a motorhome is towing another vehicle by way of a tow bar
    • If the towing vehicle has a 2-wire system and the vehicle being towed is on a 3-wire system (the vehicle has amber turn signals, separate from the brake signals), the vehicle to vehicle tail light converter will need to be used
  • This item cannot be installed backwards (the input going to the output side) to convert a tow vehicle down
  • Will not work with vehicles that have LED tail lights
  • Limited 1-year warranty

Note: You will need to install a tail light isolating diode system (38955) and 2 additional diodes (RM-792) with this tail light converter to prevent electrical feedback when flat towing a vehicle. Vehicles with separate turn signals and brake lights will need a total of 6 diodes.

118158 Vehicle to Vehicle Taillight Converter

Replaces 31820

Installation Details 118158 Installation instructions

California residents: click here

Customer Reviews

Vehicle to Vehicle Tail Light Converter - 118158

Average Customer Rating:  4.8 out of 5 stars   (130 Customer Reviews)

Used when a motorhome with a 2-wire system is towing another vehicle with a 3-wire system, by way of a tow bar.


This product works well with some thought and acknowledgement that it has limitations.

I have just bought my second one. The previous one failed after five years.

This new one etrailer recommend the use of diodes to prevent feedback to the towing vehicle.
This is not a bad idea but was not previously available.

The circuit diagram that comes with this unit was misleading to me.
Eventually I figured it out and will passon what I learned.
My trailer has separate orange indicators.
It is wired as all my trailers are with a seven way plug.

You will see each diode having three connections.
Two from the towing vehicle and one to the indicator bulbs.
I just used one of the diode input tags connected to the appropriate wire from the seven way.
The output I fed to the indicator bulbs.
I have three indicators on each side of the trailer and they can all run off of the same tab.

I am enclosing a few pictures.
The first one is the old unit which was housed in a separate box screwed to the chassis.
Then I had a second box which held all the connections.

The second picture shows the new unit contained in its own box with the five diodes used.
The box is just a plastic project box from Radio Shack.

The last picture is of the finished unit all sealed and ready to go.

Now for those limitations.
Do not expect this to work as though it were an extension of a four wire vehicle.
The indicators will work and the brake lights work BUT the indicators go off when the brake is applied.
The unit cannot run the separate indicator and the brake at the same time.

No problems so far
Peter - 10/11/2021


I gave up trying to find a wire to tap for a third brake light on a 2013 GMC Sierra, so I ordered a 2 to 3 wire adapter ( #118158) as recommended by you expert Michael H. He stated that only one of the inputs was needed, but both Left and Right turn were required to make mine work at all. That aside, the product was received quickly and installation was simple using the enclosed diagrams. I have never seen anything mentioned anywhere about waterproofing undervehicle connections. I do and they last for years.

Does the 3rd brake light flash when using the hazard lights?
-- comment by: Sam - 05/06/2015

Yes, emergency flashers will flash the third light also.
-- comment by: - 05/24/2015


This converter worked great for what I intended it for. I was wanting to add a third brake light to back of my fifth wheel trailer. I purchased STL179RB Glolight Thinline LED also. I tried to wire this direct. It won't work, it flashes when you turn the turn signal on. A friend of mine recommended this after doing a search on the etrailer website. Etrailer support recommendation was installing two lights. Duh! that's why I wanted a third brake light, I already have two lights that function as stop/tail/turn. The installation in these pictures is not complete. I was trying to avoid drilling holes in the back of my trailer, I still may have to. I am going to enclose the wires going up the trailer to the light in some white wire loom. The light at present is secured with only white RTV, not sure that will hold. I'm still trying to avoid drilling new holes, may have to though. I hooked up all the wires on the input side, white to ground, green to right stop/turn, yellow to left stop/turn. I hooked only the red wire to red wire of the light on the output side. I hooked the ground (white wire) of light to input side of converter. Yes, it works and no it does not blink when either blinker is turned on. The additional two wires on the output side of converter are not being used nor is the additional wire of the light. Sorry for the long review, don't usually write reviews at all. Anyway, if this will help even one person it will be worth it.


I use Optronics oval LED lighting exclusively and I don't think this was made to work with them because of the rapid response of the LEDs. I use this so that on a 4 wire system I can have turn signals on the side of the trailer. When you first hit the brakes, there is a fast blip of light from the side marker/turn signals. With an incandescent bulb it would be too fast to light the bulb. This is something I can live with. I think this works great with no problems so far.


First off the customer service at etrailer is by far the best that I have dealt with. If I had a question, they sent me an email response very quickly. Secondly, the shipping is extremely fast. I placed the order and it came to an APO AE address (military stationed in Germany) via USPS Priority Mail and it arrived in like 5-7 days, I was shocked when it arrived, because I was expecting at least another 3 or 4 days.

So, as far as the product. Works great and was just what was needed.
Project was to make an adapter that I could plug into my 2017 Jeep Grand Cherokee U.S. spec and use a German trailer. My friend did all of the wiring and made the adapter, so I do not take any credit for any of it. Just sharing this, to those trying to figure out if it can be done.
Moving on, the adapter is a 7 pin/blade normal American plug that goes into the back of the JGC and the other end of the adapter is the 13 pin German (European) socket. We tried it without this product and all worked except when you hit the brakes the brake lights were faded and the blinker lights were lit up as if they were the brake lights. So, had to get this product and separate the brake/blinker light on the American side and have separate brake and turn wires on the German side.
Put this product between the two in the middle of the adapter, wired it up and all works great!
I used 2 zip ties around the product and a bunch of electrical tape to hold it to the adapter, at least to give it a better look.

Now I only have to plug in the adapter whenever I use a German trailer and all works correct. When done towing, remove the adapter and everything is back to the American system. Did not have to cut/splice or do anything to the wires on the JGC or the trailer, all was done at the adapter.

Thanks again to etrailer for providing awesome customer support and shipping!


The "Vehicle To Vehicle Tail Light Converter", Item #118158 is serving my needs well. I refitted my trailer completely using all LED lights. I mounted the converter inside the "C" channel underneath my tongue mounted toolbox for a little added protection. I also soldered all connections throughout the re-wire and used heat shrink &/or liquid rubber over all connections. I feel that proper planning prevents poor performance. I ordered numerous lights from etrailer also, and all are working fine. When I chose to call them with a question about one of their products, it was answered quickly and appropriately. I am a business person, and that's customer service!

The tail light converter is still working fine. I have no regrets.
Jim R - 04/06/2021


I was looking for a way to add a third tail light to a vintage trailer and this proved to be just the ticket. Easy to install and worked great right out of the box.

Plenty of communications from etrailer staff along the way. Just wish they would provide tracking info so you could plan for expected receipt date.


Since my trailer is 100% LEDs, I would not have chosen this for the two to three wire conversion since the description specifically states "not for LEDs". But after a discussion with the tech guys, I installed it and it has worked flawlessly.


Used to add little LED marker turn lights on the corners to vintage two circuit airstream trailer. The led corner lights now are red running at night, red stopping by day and switch to yellow, when turning, day or night.


Interested in adding a third light up higher on your trailer for additional visibility? This product will separate the turn signal and brake signal on a four pin connector so you can add a running and brake light up higher to be visible. Simulates the third light that most cars and trucks have these days in the center of the back window. Positive for the semi-trucks visibility. You do not really think they can see the normal trailer lights 12" off the ground when following close behind or coming over a hill do you?
Included a picture with just the running lights illuminated.
Thank you etrailer for having the right products in stock! Most other dealers did not know what I was talking about and one even told me it was against the law. Called state highway patrol and they encouraged the additional third light! I also added the higher side running lights when semi's are merging behind you at night.


Shipping was fast. Installation was easy. Works as designed. Couldnt ask for a better result. Now my tow car is all wired correctly.


I am always able to find exactly what i need here at I put a camper shell on my tow vehicle and I had to wire up the high center brake light. I called Sal to find out if there was a device to kill the blinker signal to the light, and he knew exactly what i needed. It was an easy and pleasant experience. I highly recommend Sal, he is very knowledgeable and easy to work with. Thank you for the great service!


I used this to change the wiring and harness on a European trailer to work with my standard US 4-pin trailer outlet.
Pretty simple and straight forward with the diagrams and write-ups that I found on this site.

The parts are still on my European trailer and working well! The trailer is a German brand and started its life there in Germany being pulled by my American-spec Jeep Wrangler. The trailer’s wiring and the Jeep’s connections needed to be massaged in order to work. The parts I ordered from etrailer and the writeups for the project on your site made it all possible. Now the trailer is titled and registered in Virginia and enjoying its life on this side of the Pacific!
Aaron - 03/27/2019


This is the second time I have purchased tow brackets and wiring kits from etrailer. Wouldn't buy from anyone else. They know their stuff.


Perfect for connecting the tail lights from my RV to my car on the car dolly.


Great service on a part I wasn't aware was available. Was going to use a 7 pin adapter to power seperate lights on a little camp trailer. This will simplify my needs.


This product was used to separate the brake light signal from the turn light signal on a Ford F-350 cab/chassis with a flatbed to facilitate using amber turn signals without them illuminating when the brakes are applied (truck only, no trailer). So far they are "functioning as designed" and I'm very happy with the product.

Still working fine.
Gregory V - 10/09/2019


I installed a European 13pin receiver on a 2018 Ford Explorer and stowed the wiring adapter under the vehicle. Worked flawlessly so far with caravans and bike carriers.

Still working flawlessly, even with lots of snow, ice and sludge
Christian G - 03/01/2021


Works great hooked it up on my Ford truck to split up the turn signals and the brake lights on my trailer


Fairly easy to install, and worked as e xpected.

No problems, so much better than a tow dolly of past years. Used it on several trips without problems.
Ronald - 02/25/2022


This is a very useful device for those of us who flat tow auxiliary vehicles, such as a tracker behind a motorhome or whatever. Also it is easy to install. Keith

converter works well. I have had no problems. I use dielectric silicone grease on all connections.
Keith K - 07/15/2018


Unfortunately this did not work for my purpose, not that the product was at fault. I was trying to retain the amber turn signals on my vehicle when flat towing but what I found is the Motorhome already has a taillight converter in the system because it too has amber turn signals. the two converters did not get along. I had to remove it and rewire to combined signal and brake lights


I have used etrailer many times and have always been satisfied. If you need parts for campers, towing, etc., this is the place to go.


Still working great!
Install was easy,
their online help and install videos make installation a breeze.


Easy painless installation!
I used
this product to install a third brake light on my TC Teardrop camper.

Show More Reviews

See what our Experts say about this Tow Ready Tow Bar Wiring

  • Using Two Wire to Three Wire Converter Part # 118158 to Provide Third Brake Light for Trailer
    Using the Tow Ready Tail Light Converter, part 118158 should do the trick for you. If you are wanting to leave the existing tail lights on your trailer operating as both directional and brake lights, you would tap the green and the yellow wires of the converter into the appropriate wires leading to the tail lights. The red wire exiting the converter would then be used to power your third brake light. The yellow and green wires exiting the converter would not be needed, simply cut them...
    view full answer...
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  • Where Do Extra Diodes Go When Wiring A Tow And Towed Vehicle With Separate Brake And Turn Signals
    The other two diodes are needed so you can have separate turn and brake signals. So you will have a diode for each brake light (right and left), a diode for each turn signal (right and left) and a diode for each tail light (right and left). I will send you a link to the wiring diagram of the # RM-154 wiring kit to show where all of the diodes are connected and what color wires go to what function on the tow vehicle. A separate wire for the brake circuit will have to be run on the towed...
    view full answer...
  • Can a Tail Light Converter be Used to Put a Third Brake Light on a Trailer
    Using a Tail Light Converter, like # 118158, will work to isolate the brake light signal for a third brake light on your trailer. What you would do is connect the green and the yellow wires on the input side of the converter in line with the appropriate wires leading to the left turn/brake and right turn/brake lights. The red wire exiting the converter would then be used to power your third brake light. The yellow and green wires on the output side of the converter would not be needed...
    view full answer...
  • Tail Light Converter for Towing a Trailer w Separate Tail Light Wiring with a Vehicle with Combined
    You will want to use a Taillight Converter # 118158. You would wire up this unit into the wiring of your trailer. The input side of this will be run from the trailer 4-way, and the output side will go to the wiring on the trailer. Check out the video I attached that details the installation of this product. The terminology used in this video will be different because its talking about using this product for flat-towing a vehicle with another vehicle. However, if you wire it up the way...
    view full answer...
  • Vehicle to Vehicle # 18158 Taillight Converter for Separate Turn Signals on 2003 Jeep Wrangler
    For what you are trying to accomplish, you shouldn't need the diodes. The # 118158 vehicle to vehicle taillight converter you referenced would convert the 3 wire system you have now to the 4 wire system you want. Diodes are for use when one vehicle is towing another, and you don't want the signal from the towed vehicle feeding back into the electrical system of the tow vehicle. I'd recommend installing the converter in an interior location if at all possible. The converter isn't designed...
    view full answer...
  • Wiring Side Marker Lights on Trailer as Turn Signals
    Using a relay would be the way to go if you wish to use those fog lamps as reverse lights. You would want one input on the relay tapped into the reverse light circuit, and one leg ran to a 12-volt power source. There would be no really simple method of getting a side marker light to serve as a directional signal without having it light when the brakes are applied. How to make your connections will depend on the taillight system of your tow vehicle. If your vehicle has amber colored turn...
    view full answer...
  • Wiring Side Markers On Trailer as Turn Signal Using Vehicle to Vehicle Converter, Part # 118158
    You could use the vehicle to vehicle tail light converter, part # 118158. You would tap the input side of the converter into the right and left turn circuits on the trailer, and run the right and left output wires to the side markers you are wanting to use as turn signals. The brake wire on the output side would not be used, just cut it short and tape off the end so it does not short out on anything.
    view full answer...
  • Will Vehicle to Vehicle Tail Light Converter # 118158 Work to Power a 3rd LED Brake Light
    You can use the vehicle to vehicle tail light converter # 118158 to power a third brake light whether it be LED or incandescent. The input green wire will connect to the combined right turn/brake light circuit and the yellow wire will connect to the combined left turn/brake light circuit. White gets grounded to the vehicle or trailer frame. On the output side if you just need the brake circuit it is the red wire. The green and yellow output wires can be capped off and stowed out of the way.
    view full answer...
  • Can the Tow Ready Vehicle to Vehicle Taillight Converter be Used on a Boat Trailer and Get Wet
    The Tow Ready Vehicle to Vehicle Taillight Converter, # 118158, is typically used on motor homes that are towing another vehicle by way of tow bar. The converter is not a sealed box so if it were to be submerged in water or exposed to rain, it would be damaged. If you choose to use this part on your boat trailer, you will want to make sure that the converter is mounted in a location that protects it from water.
    view full answer...
  • Are Diodes Required to Separate Brake Lights from Turn Signals Using Converter 118158 on Trailer
    That is exactly what converter # 118158 was designed for. You will not have to use diodes, although you could if you wanted and it wouldn't hurt anything, because there is only one input circuit for each of the wires. The red output wire would go to the brake light wire on each tail light. Yellow would go to left turn signal and green would go to right turn signal.
    view full answer...
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  • Converter Box Recommendation for Converting Combined Signal to Trailer with Separate Lights
    Yes, the Vehicle to Vehicle Taillight Converter # 118158 would work well to separate the combined turn signal circuits from your 2012 Subaru Outback with combined wiring to the separate wiring of your trailer. This would be the only product you would need. Basically, you would want to mount this product somewhere near the connector on your trailer and then splice the wiring in. The box is labeled to let you know exactly which wire goes where, but you will need to run the right turn/stop...
    view full answer...
  • Converter Recommendation for Vehicle with Separate Turn Signals to Connect to Trailer with Separate
    Sounds like you are trying to install a 4-way trailer wiring harness on a vehicle that has brake lights separate from the turn signals. Since the trailer has these two circuits combined on one wire you'd need a converter to allow you to accomplish this. Since it sounds like you have 4-way connectors already you'd just need to install the correct adapter which is part # 118158. You'll need to install this on the vehicle side of the 4-way wiring. I attached an install video for this kit...
    view full answer...
  • Why are Diodes Needed for Lighting when Flat Towing a Vehicle
    When a vehicle is being towed it cannot operate its own lights. The diodes are a gateway with 2 inputs and one output. One input is the regular wiring on the vehicle. The other input is from the RV. Since vehicles being flat towed will not have working lights they will have to get power to function from the RV. The diodes allow for 2 inputs so that you don't have to disconnect the vehicle lights to plug in power wires from the RV. The tow vehicle lighting system only matters if the tow...
    view full answer...
  • Adapter Recommendation to Separate Out Vehicle Combined Lighting Circuits
    Yes, if you needed a converter to separate out a combined trailer lighting circuit the part # 118158 would be the correct adapter to do this.
    view full answer...
  • Recommended Converter for 3rd Brake Light on Removable Camper Shell to Function with 4-way Trailer
    The removable camper is not wired correctly, but should still be giving you light. The ground wire of your light should be tied into the white ground wire of your trailer connector. The red power wire of your light should be connected only to a 3rd brake light wire or isolated wire that is not found in your 4-way trailer wiring harness. The brown wire is for running/tail lights not brake/stop lights. To separate this out, you can use the Vehicle to Vehicle Tail Light Converter # 118158....
    view full answer...
  • Installing Side Trailer Lights to Blink with Corresponding Turn Signal
    If you are wanting to install side marker lights on your motorcycle trailer that blink with the turn signal, it will need to be tapped into the turn signal/brake light wire for that side. However, just doing this will also allow the side light to come on with the brake lights. You do not want to attach it to the running light circuit, as this would back feed and force the lights to come on when they should not. Trailer have combined turn signals and brake lights and the running light...
    view full answer...
    Image 1 for
  • Converter Needed to Run Separate Taillight Wiring on Trailer
    Standard trailer wiring has the turn signals and brake lights combined. The only time we see separate is if someone decides to use a converter on the trailers wiring to separate the signals and run dedicated brake lights. For that you'd need the part # 118158. See install video below.
    view full answer...
  • Does a Tail Light Wire Get Connected to Vehicle to Vehicle Tail Light Converter # 118158
    The brown tail light wire would bypass converter # 118158. The only connections that get made to the converter are the combined left turn/brake light and right turn/brake light. It can be grounded to a bare metal surface or to the ground in the wiring harness.
    view full answer...
  • Trailer Wiring Converter Recommendation for Adding Third Brake Light to Trailer
    You have to use a taillight converter like the part # 118158 wired to your trailer's wiring so that you can seperate out the stop light from the turn signals. Once you do that the red wire of the box will have just the brake signal for you power the third brake light. It will not blink with the turn signals.
    view full answer...
  • Does Bar Light at Rear of Trailer Typically Carry Running Light or Stop Light Circuit
    Most likely it's a running light. Typically a center bar is a clearance light that runs to the running light circuit. Wiring in a third brake light to a trailer is somewhat involved as you have to use a signal converter like part # 118158 to separate out the brake circuit from the turn signals. I attached an install video for this converter for you to check out as well.
    view full answer...
  • Taillight Converter to Separate Combined Taillight Circuits
    The taillight signal converter part # 118158 that you referenced would be the correct product you would need to convert a combined taillight circuit to a separate circuit. The turn signals would only be illuminated when the blinkers are applied on the tow vehicle. They would not stay on all the time. Check out the review video I attached as well.
    view full answer...
  • Brake Lights are Dim With Turn Signal Flashing Using Converter 118158 On a Trailer
    The LED light warning is in reference to flat towing a vehicle that has LED lights. So basically for your situation the trailer (vehicle) LED lights could be the issue. An easy way to determine if it works better with incandescent bulbs would be to replace an LED brake light with an incandescent light of some kind and see if the problem persists. If it does persist then the issue could be related to the fact that converter # 118158 is not rated very high. This is just the nature of this...
    view full answer...
  • Turn Signal Causes Supplemental Braking System to Apply Brakes on Towed 2004 Honda CRV
    Sounds like you are going to need a Vehicle to Vehicle Tail Light Converter like # 118158. This converter is used when a motorhome with a 2-wire system is towing another vehicle with a 3-wire system, by way of a tow bar. If your supplemental braking system is spliced into the right turn signal (for example) then you will take the converter's green wire and splice it into the right turn signal wiring and run the red wire to the supplemental braking system.
    view full answer...
  • Converter Recommendation for Separating Trailer Turn Signal Circuits from Brake Lights
    7-way trailer wiring is not designed for giving you a dedicated brake light circuit as standard trailer wiring has the stoplights and turn signals carried on the same circuit like you have found. I attached a picture that shows how a 7-way is typically wires. You could rewire your trailer and vehicle to carry the circuits any way you wish, but typically sticking with the standard diagram is the best and then to convert from separate to combined circuits you'd want to use a converter like...
    view full answer...
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