Troubleshooting Running Lights That Go Out When Brake Lights Are Activated

Question:

Running lights on step on brake pedal lights cut out

asked by: Joe

Expert Reply:

It sounds like you may have a weak ground connection on your vehicle's trailer wiring harness. A bad ground can cause all sorts of odd effects, including having one light function go out when another is activated. A weak ground will pass enough current for some functions to work, but possibly not for others.

Check that the wiring harness ground wire's ring terminal is tightly attached at a clean bare metal surface on the vehicle. You may want to clean/sand that spot to ensure metal-to-metal contact between the ring terminal and the vehicle. If its easier you can relocate the ground terminal to a new spot that provides better contact, but be careful where you drill to avoid damaging anything behind that location. If you prefer you can run a secondary ground jumper wire from that same grounding point directly up to the battery's negative terminal.

expert reply by: Adam R