Why do my trailer brake lights work but not running lights?
Why do my trailer brake lights work but not running lights? Trailer Running Lights Do Not Work but Brake Lights and Turn Signals Do Work. If the issue is not a fuse or relay then you can test the vehicle side trailer connector using a circuit tester such as # 40376. Turn the vehicle headlights on and use the circuit tester to test the pins on the connector at the back. Why are the brake lights on my trailer not working? Running jumper wires from the light grounds to the main trailer connector ground can help. And finally, if the...