What is the Function of the Yellow/Brown Wire on a Trailer

Updated 08/26/2024 | Published 03/10/2014

Question:

Have as ram 2013 with factory tow wiring 7 pin rv and 4 pin rd.Trailer was wired with 7 pin but only had 4 wire hooked up. yellow / brown wire to left turn brake .green /brown to right turn and brake lights. white to ground.So I installed my trailer brakes and grounded one wire to the frame ,run the blue wire up to the new 7 pin connector,The trailer green/brown and yellow /brown wires come up from the rear and tie into the side running lights using the the green / brown wire only. Running to the trailer connector7blade curt non sae which plugs into to the truck will be the yellow brown and well as the yellow wire. At the new connector the blue goes to the blue,trailer brakeswhite to white ground green/brown to the brown running lights. yellow to right turn signal and green to left turn signal ..Where the Hell is the yellow/brown supposed to go? The right turn signal or the brown running lights?

asked by: Gene

Expert Reply:

Your yellow/brown wire most likely ties into the brown running light wire. Typically, when a trailer has a green/brown wire and a yellow/brown wire, they are both used for the running light circuit. The green/brown wire is ran down the right side of the trailer and the yellow/brown wire is ran down the left side of the trailer for the tail lights and marker lights. This prevents the need from running jumper wires across the trailer for the running lights. If your trailer is setup this way, you can tie the yellow/brown wire into the green/brown wire or the brown wire at the trailer connector.

expert reply by: John H

Nora C.

2/18/2024

I am trying to connect a homemade trailer to a 7-pin control box. I have a brown/yellow and a brown/green and another brown wire. I tried attaching the b/g to the right turn/stop (brown on the 7 pin controller) and the y/b to the left turn/stop (red on the 7 pin control box). This does nothing, no power to anything. And then what is this extra brown wire for?

John H.

2/19/2024

@NoraC These are always fun puzzles to solve. It sounds like you started exactly where I would start. The next step from here is to get a 12v battery and probe each of those wires to see which lights turn on. I'd take an insulated wire, connect it to the positive battery terminal. Ground the negative battery terminal to the trailer frame. And use the wire from the positive terminal to probe each wire on the trailer and see which lights come on. Then label your wires based on which wires activate which lights.

Daniel Y.

8/25/2024

My trailer has a. 4Point plug w/ white,green, yellow and a yellow/brown wires, connecting to a 4 point plug w/ a white, green, yellow, & brown wires!! Where does the brown/yellow wire connect???

Kevin C.

8/26/2024

@DanielY Typically the white is your ground, green is your right turn/stop, yellow is your left turn/stop and brown is your running lights. Manufacturers aren't always the best about following a standardized color code so you can plug the connector into your tow vehicle and test each wire with a circuit tester # PTW2993 while activating the light functions in the tow vehicle to see which wire lights up with power.