Troubleshooting Trailer Left Turn Signal Thats Not Working

Question:

We have lights in truck and trailer. Just NO left turn signal on trailer.

asked by: Shelley

Expert Reply:

Without knowing the year, make and model of the vehicle, I can't really provide any specifics but I can provide you some general things to check.

The first thing you'll want to do is determine if the problem is in the vehicle or the trailer wiring. The easiest way to do this is to plug in another trailer if one's available and see if the problem persists. If this isn't possible, use a circuit tester like part # PTW2993 on the trailer connector on the tow vehicle. Activate the left turn signal, and use your circuit tester on the socket fed by the YELLOW wire as shown in the provided photo. If you get signal on this pin (or everything works fine with a different trailer attached) you've proven that the wiring problem is on the trailer. You'll need to trace the left turn circuit on the trailer. Begin at the trailer connector on the trailer. Examine it for corrosion or damage and clean or repair if needed. Trace the wire for the left turn circuit (usually a yellow wire) from the connector back to the left turn signal lamp. Look for pinched wires and loose connections. At the lamp, check for a rusty bulb socket.

If the left turn signal socket is dead on the trailer connector on the vehicle, how you'll proceed will depend on the vehicle and whether or not the vehicle has a factory tow package or the trailer connector was installed aftermarket. In the meantime I'll link you to our trailer wiring troubleshooting article and if you can reply with the year, make and model of the vehicle, I'd be happy to help you further.

expert reply by: Mike L