Installation of New 3 Wire Trailer Lights on Trailer with 2 Wires

Updated 04/18/2018 | Published 04/17/2018

Question:

I purchased trailer lights separate from trailer wiring. Trailer wiring has two wires to each side Brown and Green one side Brown and Yellow the other. Trailer lights have three wires Black, Green and Red on both sides. I have tried all different types of connecting but all I can get to work is the turn signal and brake lights. The running lights dont come on no matter what I try. What am I doing wrong? Please help!

asked by: Gary W

Expert Reply:

I didn't find an order from you so I can't tell you exactly what each wire color is on the lights you have for sure. On your trailer, brown is traditionally the running light circuit, yellow is left turn and brake, and then the green is right turn and brake. You can test your trailer's wiring with a circuit tester, like part # PTW2993, when engaging each function to be sure.

The extra wire on your lights is either a ground wire or the turn signals and brake lights are separate. Since you don't have anything with the new lights telling you which wire is which you can test them before installing them by connecting the wires to a 12-volt battery. Unfortunately, there's going to be some guessing involved to start with but if you get one function to work then the ground wire is the same and the third wire will be the other function.

If you did order the lights from us or you can tell me the model number and manufacturer of the lights I might be able to determine the correct wire function for you.

expert reply by: Charles S