All Trailer Taillight Functions Work Except Running Lights
Updated 07/21/2025 | Published 05/24/2016
Question:
No running lights on trailer got power coming out of both trucks got everything but running lights even put a new connector on still nothing follow the line up to the junction box where it meets the wire going to lights and got power there as well it gets lost someplace in trailer Could it be a grounding issue?
asked by: Slade W
Expert Reply:
This could certainly be a grounding issue. When a circuit does not have a sufficient ground, it can cause many different issues. If possible, I recommend checking all of the grounds for your trailer taillights. You will want to make sure the ground has contact with a bare, clean, metal surface of the trailer frame. If there is any rust or corrosion at the light ground, try relocating the light grounds to a suitable location.
Another possibility is that the wire for the running light circuit has been damaged between the junction box and the taillight. If the wire has been pinched, torn, or damaged, then the running light circuit is likely not reaching the light. You can test the wires on the back of the taillights that carry the running light signal with a circuit tester, # PTW2993, to see if they have signal behind the light housing. If there is no signal on the wire here, then it is likely the wire is damaged somewhere along the trailer. Try tracing the wire as much as possible from the junction box to the taillights. If you are able to find the damage, replacing the damaged section of wire will complete your trailer's running light circuit again.
If this does not provide a solution for you, feel free to let me know and I will be happy to provide further troubleshooting steps for you.
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on Trailer Wiring
Tony
7/20/2025
ALL MY LIGHTS WORK BUT THE RUNNING LIGHTS.