Troubleshooting Trailer Light Installation Where Wires Don't Match

Updated 07/23/2021 | Published 07/20/2021

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16 Gauge, 4 Conductor Bonded Parallel Wire - Per Foot

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Hook Probe Circuit Tester

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Question:

My new lights on trailer has black an red , I need to know witch colors go to red and what to black ? My harness has red , green , yellow , white black

asked by: Shayne

Expert Reply:

The color of the wiring isn't always correct in telling you the function of the wiring; unless you wired the harness yourself and know the functions, you'll need to test the harness and figure out what wires provide power on the circuit you're seeking to install the lights on using a circuit tester like the # PTW2993. Typically green and yellow will correspond to the turn signals, white is the ground and brown is the running light circuit; red and black typically aren't found in 4 or 5 wire trailering wiring harnesses and only on 7 way RV/trailer plugs.

When it comes to your lights, and having no idea what lights you are using, I would assume that the black is the power, the red is for a blinking circuit and the lights are self grounding. If you can clarify a bit on the type of lights you've got and the trailer wiring you're using I can provide a bit more targeted information on this. I've also linked some helpful articles we did on trailer wiring that have some diagrams you may find helpful.

expert reply by: Erik B