Troubleshooting Trailer Right Turn Light That Stops Working When Running Lights Are On

Question:

my right directional light light works fine , but when i turn on my running lights it does not work, seems like the light is brighter than the left light when running lights are on , what are your thoughts ??

asked by: Doug

Expert Reply:

The lighting issue you describe sounds like a classic case of a bad ground connection.

Since running lights remain on continuously (rather than blinking like turn signals or being on only momentarily as with brake lights) they tend to draw more power. This higher current demand will cause a weak/loose ground issue to show up once you turn on your running lights even though the other functions will work okay on their own.

What you can do is check your main ground wire on the trailer. This is the wire that runs from the 4-pole or 7-way trailer connector to the trailer frame. This connection must be very solid and made to clean bare metal point on the frame for metal-to-metal contact. You can sand off any paint or primer that may be on the grounding point, re-secure the ground wire ring terminal and protect that connection with dielectric grease # 11755.

You can repeat this same ground wire check on the vehicle's trailing wiring harness. It too will have a ground wire (again usually a white wire) that must be firmly connected to clean bare metal on the vehicle frame.

The two linked articles will be helpful if you need additional help.

expert reply by: Adam R