Trailer Running Lights Do Not Operate But Brakes and Turn Signals Do

Question:

I have turn signals and brake lights on my trailer but no taillights for night all fuses are good and all lights on the truck work

asked by: Jeff

Expert Reply:

The first thing to check is the trailer's ground wire. It is not unusual for a trailer with a weak ground to still allow certain lighting functions to operate normally but not others. The Stop and Turn signals (carried on the yellow and green wires typically) are not on all the time and so their current draw is less than that for the running lights which stay on all the time when your vehicle headlights are on. A weak ground may pass enough current for the stop and turn signals but still be unable to handle the always-on running lights.

Make sure the ground wire from the trailer connector is firmly attached to a clean bare metal surface on the trailer frame. If there is paint, grease or rust on the grounding point then you can sand and/or clean that spot before re-attaching the ground wire.

You can also inspect the trailer connector's pins for the running light circuit and ground for signs of even slight greenish or whitish discoloration that could indicate corrosion. The linked article will help your troubleshooting efforts.

expert reply by: Adam R