Troubleshooting Trailer Wiring that Taillights Wig Wag When Either Blinker is Applied

Question:

I picked up a used utility trailer. It needed lights. I picked up a trailer light kit from the local hardware store. I wired it up, and connected it to my vehicle to check the lights. I have tail lights, but no brake lights. When I put the turn signal on, either left or right, both tail lights wigwag. This is just the standard 4pin flat plug setup, nothing fancy. Wiring mistake at the light, or would it just be easier just to start over and redo it?

asked by: Jim W

Expert Reply:

First thing to check is the grounds of the trailer lights. Insufficient trailer taillight grounds are notorious for causing seemingly unexplainable taillight behavior like what you described.

Make sure that the trailer side connector are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. 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: Jameson C