Trailer Right Turn Signal and Brake Light Not Working After Installing a 4-Way Wishbone Harness

Updated 11/09/2015 | Published 11/07/2015

Question:

the flat 4 way on my 2013 ram pick up works fine on my other trailer. It was wired using a standard flat 4 way harness. I bought a Tractor supply trailer it has a flat 4 prong 5 wire wish bone harness. when it is plugged into the truck I get running lights, left turn and brake lights. but no right turn or brake lights? this has been like this from the moment I bought it. I went back to Tractor supply and hooked up two of there trailers on the lot and had the same problem? They had no idea how to help me. I did not want to have to re-wire the brand new trailer I bought but unless you know what is going on with this , I have run out of ideas. It may have something to do with the factory combo plug on my truck? but as i said it works with every other trailer I own. thank you for your time and consideration.

asked by: Richard

Expert Reply:

A wishbone harness will have 5 wires associated with 4 pins. First is the ground wire, usually white. Next to that there are 2 running light wires. Both have to be connected to the running light wire. It has 2 running light wires so you won't have to run a jumper from one side of the trailer to the other.

If the trailer has a single running light wire then you would splice those two running light wires together and splice them to the single trailer wire. Or just use one of the wires and tape up the other one. They are usually brown with a stripe.

Next to the running light pin is the left turn signal/brake light circuit, usually yellow, and then the right turn and brake light pin, usually a green wire. I have included a link to a video that should help.

Also make sure that the main trailer connector ground and the ground for all of the lights are attached to clean and corrosion free bare metal surfaces.

expert reply by: Michael H