What are the Red, Black, Green, and White Wires on a Trailer for

Updated 10/14/2025 | Published 08/18/2018

Question:

Helll! I have a 4 wire connection. The colors on my trailer are red,black, green and white. I am wiring a new 4 Way plug on and the wires are white, brown, yellow and green. I was wondering what colors to match up? Thanks for the help!

asked by: Chris

Expert Reply:

In regards to the 4-way wiring harness you are trying to install; the white wire is for the ground, the brown wire is for the running lights, the yellow wire is for the left turn/brake light, and the green wire is for the right turn/brake light. Unfortunately, the only way to know for sure what is on the trailer would be to test them with a circuit tester.

I have attached our wiring help article for you as well which may help but you will need to test regardless.

expert reply by: Conner L

David

10/11/2025

What is red for?

Nick S.

10/14/2025

@David You would need to test the wires with a circuit tester for function. Since the standard configuration is the white, brown, yellow and green I am not sure what they would have made the red wire. So you would just need to test for function and then match it to the other harness. White being ground, brown is running lights, yellow is left turn/brake light, and green is right turn/brake light.