Troubleshooting Left Side Turn Signal Not Working On Trailer

Updated 06/15/2015 | Published 06/12/2015

Question:

I have two brake, lights, driving lights, and one right turn signal on my trailer, but the left one is solid. When testing with a 12 voltage tester, it shows a continuous circuit, not a flashing one, all the way to the truck the right turn turn signal tests as blinking all the way through. Changed a relay and fuse in the truck, but no go.

asked by: Scott M

Expert Reply:

This sounds like a ground problem on the left side. With the brake lights there is a constant signal coming through which is enough to make the lights illuminate on both sides like they should. But the on/off of a turn signal does not offer enough consistent voltage and makes the problem apparent.

First check the grounds on the side where the problem is. Trailer lights usually ground through their mounting studs unless there is an obvious ground wire. In either case, the ground will need to be attached to a clean and corrosion free bare metal surface.

You can also make sure that the main ground from the trailer connector is also connected to a clean surface and that the connector itself is free of any dirt or corrosion. Make sure to check the vehicle side connector too. If you find any loose connections, broken or frayed wires, those will need to be repaired as well.

expert reply by: Chris O