Troubleshooting Trailer Running Light Assembly Not Functioning on Trailer Wiring

Question:

All passenger side trailer lights work and drivers side brake, blinker, and emergency flashers work ... only the drivers side tailight/running light on the trailer is not working ... has to be a problem with the brown wire to the drivers side tailight/running light ... right?

asked by: Larry B

Expert Reply:

Actually the issue you described sounds like a weak ground on the driver side taillight assembly since it doesn't work when the running lights are on. This circuit draws the most amperage since the most lights come on with it activated so if a weak ground was going to prevent a circuit from working it would be this one. Check the condition of the ground on the assembly. Most likely you'll find it needs to be cleaned or ran to a more solid portion of the trailer frame. Running a jumper wire from this circuit back to main ground of the trailer wiring is also something that will help.

I also attached a link to a page that covers troubleshooting trailer wiring as well.

expert reply by: Jameson C