Trailer Left Turn Signal Not Working But All Other Lights Work Fine

Question:

WHEN HARNESS IS HOOKED TO BOAT TRAILER ALL LIGHTS ARE WORKING BUT LEFT TURN SIGNAL ANY IDEAS THINKING ITS THE BOX THANKS

asked by: BILL

Expert Reply:

You can determine where the fault is by doing a little testing using a circuit tester such as # PTW2993. First disconnect the trailer from the tow vehicle. Then use the circuit tester to test the functions of the vehicle side connector while someone sits in the vehicle and operates the light functions.

If the left turn signal does not work at the 4-Way, then test the yellow wire leading into the converter box from the vehicle. If that wire does have the proper signal when the left turn signal is activated but it is not working on the 4-Way side, then the converter is bad, and the harness will have to be replaced.

If everything is working on the vehicle side, then the issue must be on the trailer. Make sure the trailer side connector is clean and free of corrosion and that the main ground is attached to a clean and corrosion free bare metal surface.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by: Michael H