Troubleshooting No Power to Running Lights and Tail Lights

Updated 04/15/2024 | Published 04/13/2024

Question:

I have a brand new harness, 4 pin flat with green, yellow and two brown wires. I have one running light on each side new and rear lights new. I have spliced the running lights into each of the browns with shrink wrap connections and matching wire connections on the lights also with shrink wrap connections. None of the lights came with a ground wire however, the white wire from the harness has been connected to a clean bare metal spot on the tongue. I have checked the truck fuses and the harness on the truck, all are working. I have also checked the wires coming out of the harness with a grounded probe and there is power however no power just before the running lights, after the running lights and before the rear lights. No idea what to do now.

asked by: John P

Expert Reply:

The new lights you have should ground through the mounting hardware since they don't have a ground wire. As long as the mounting hardware runs into the frame or metal that contacts the frame that should be fine. You can run a separate wire if you want just to be safe.

Since you have power running to just before the lights I'm also not sure what the issue would be aside from a bad ground. I would double check the light installation before moving on to something else. You might also want to try removing one of the side running lights from the equation to see if that fixes it on that side of the trailer. If you reconnect it to only run to the rear lights and it works that narrows down the problem.

expert reply by: Robin H

John P.

4/15/2024

Thanks Robin, it was a grounding issue. The bolt on the light was too small so I added a ground wire from the bolt to the frame an it worked. Appreciate the help.