Troubleshooting Trailer Running Lights That Flicker and then Turn Off

Question:

When the running lights in the car are turned on, the running lights on the trailer come on for 1 second and shut off. Brake lights and blinkers work perfectly. Cannot get the lights to work for use at night. Neither the yellow markers lights nor tail lights will stay on when the car running lights are turned on. they blink once and shut off. any thoughts as to why this happens? Thank you

asked by: Tom P

Expert Reply:

Sounds like it could be a ground problem, the additional load of the running lights being on your vehicle is too much for the weak grounds and the circuit is shutting off. Or the problem is your trailer taillight circuit is drawing more amperage than the wiring harness is capable of handling. You might try disconnecting a few of the running light circuit clearance lights to see if this allows the lights to illuminate. If so, you will need to convert your trailer to LEDs. I attached a link to a page that has all of the LED trailer lights we carry.

Follow the wiring harness from the trailer connector, and make sure the white ground wire connects securely to the trailer frame, and that this ground connection is not corroded. Trace the running light circuit, which is typically a brown wire from the connector toward the rear of the trailer. Look for pinched wires or loose connections. Make sure that all the wire insulation is in good condition, with no cracks or worn spots that would allow the copper conductor to short out.

Each individual side marker and tail light will either ground via a separate ground wire, or through its mounting stud being in direct contact with the trailer frame. If a marker light that grounds through its stud (like the one you mentioned) is attached to plastic or wood or a metal place that is not in good solid contact with the trailer frame, you will need to run a separate ground jumper to the trailer frame to maintain a continuous ground circuit. Make sure that the grounding point for each lamp (whether it be the mounting stud or separate ground wire) is securely fastened to the trailer frame, and that the connection is not corroded.

I have linked you to or Trailer Wring FAQ article. The article contains wiring diagrams and troubleshooting strategies that you might find helpful.

expert reply by: Jameson C