Troubleshooting Left Turn and Running Light Signals Not Working on Trailer

Question:

I know it is a problem from my vehicle because it works on my second My left signal and running light do not work But the left signal works when I put the hazard lights on

asked by: Suatin

Expert Reply:

It does sound like your trailer lights are okay and the vehicles are the problem, but it is easy enough to test each. First, check the fuse for the left turn signal and left running light as these are typically on different circuits than the hazards. That could be the issue.

You can make sure the trailer's lights function correctly simply by disconnecting it from the vehicle and applying 12V power directly to each one of its circuits, one at a time, using the vehicle battery or a spare battery that is well-maintained with a charger like # CTEK56353. If the trailer lights operate when powered in this way you know they are not the problem.

On the vehicle side you will use a circuit tester like # PTW2993 to test the circuits on the vehicle 4-pole wiring harness. Ground the tester and check each pin, one at a time, while a helper sits in the vehicle and activates the turn signals, brake lights and running lights.

expert reply by: Adam R