Troubleshooting Trailer Light Malfunctions - Running Lights Not Working  

Question:

Expert Reply:

If the turn signals are working properly, but the running lights aren't it could be a short, blown fuse or a ground problem. I would first test the trailer connector on the truck. After that I would check for blown fuses.

Next I would check to see if the ground wire on the trailer is grounded to an appropriate metal surface and not aluminum. You may need to run a jumper wire to a better grounding metal surface.

Boat trailers are often equipped with fold away tongues, this may also be causing the ground problem. To resolve this you may also need to route a jumper ground wire.

Check the ground and the connectors on the vehicle trailer wiring connector that you are using to tow your boat trailer. If the problem is only when the running lights are activated, and those require the most power, the issue is related to an incorrect ground. You will need to make sure that the trailer connection points are not corroded, bent, or damaged. Also make sure that the vehicle ground for the connector is properly grounded.

I have included some helpful articles that show traditional trailer wiring diagrams, explain trouble shooting trailer wiring, and connection points.

expert reply by: Chris O

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