Troubleshooting Trailer Taillights that Stop Working When Brakes are Applied

Question:

Hi there. When testing all the lights of my trailer with a battery charger all lights operate perfectly. When connecting it to my car all lights do work but the brake light will illuminate briefly then go off.??

asked by: Jan J

Expert Reply:

Sounds like you either have a weak ground on your trailer taillights or the lights themselves are drawing too much amperage and it's causing the circuit to just shut off. Typically a fuse would get blown if this were the case so most likely it's a weak ground.

Also, be sure to check the function with the engine of the tow vehicle running as the additional amperage of the alternator running will give the trailer circuits a bit more juice.

expert reply by: Jameson C