Testing Trailer Wiring Circuits to Determine what Wires Run to Running Light Circuit

Question:

On my trailer I have the yellow and red on the left and the green and brown on the right how do I connect the side light which only has a ground and a black wire to my left side, do I connect the black to Red or do I connect the black to the yellow on that left side to maintain running lights and brake lights ? Thanks?

asked by: Brian

Expert Reply:

You are going to need to verify what the circuit each of the wires you have on your trailer carries first since not all of the wire colors you mentioned are standard. Use a circuit tester like part # PTW2993 to test them while the different taillight functions are applied. The circuit that is hot when the running lights of the vehicle are on is the circuit to use for the running lights.

I attached a help article that has standard trailer wiring diagrams for you to check out as well.

expert reply by: Jameson C