Troubleshooting Trailer Lights With 3 Wires Connection to 4-Wire Trailer Wiring Harness

Question:

My plug has 4 wires and my trailer lights only have 3 out of each side. How do I connect?

asked by: Bill

Expert Reply:

Your plug wires will have running light, stop and turn light for each side and then a ground connection. Your trailer lights with 3 wires will either have separate stop and turn lights or a separate ground wire instead of using the mounting hardware as ground. You will want to use a battery and jump wire to test your trailer light wiring unless it is obvious based on the light bulb sockets. If the wiring is connected, you can use a circuit tester like # PTW2993 to probe the insulation on the wire to test function. I've attached an article to assist.

If you have separate stop and turn functions on your trailer, then you can use wire converter # 118158 to separate the turn signal from the brake light function.

expert reply by: Jason S