Troubleshooting Trailer Running Light that Stops Working with Head Lights

Question:

When the headlights are in auto everything works correctly during the day. If I turn on the headlights everything works OK except the left turn signal. It will not operate correctly.. I dont know what happens when the auto mode detects darkness and turns on the headlights. I suspect the same. Thx

asked by: Greg C

Expert Reply:

What you described is a classic weak ground scenario. When all of the vehicle and trailer lights are on you are drawing quite a bit more amps so any ground weaknesses will show up. I know your headlights are on all the time but it's not till the headlights are manually turned on do all of the running lights of the trailer and vehicle activate.

What you need to do is improve the ground of the light assembly that's not working properly and you'll see it come on like it should.

You can also run a ground wire from the light back to the main ground wire of the trailer and that will help too.

expert reply by: Jameson C