Left Brake and Turn Signals on Two Different Trailers are Not Working

Question:

All my trailer lights work my left turn signal and break is not coming on on two different trailers All fuses good new 7 round to 4 flat just had truck wiring addressed at hitch shop 45 days ago any suggestions.

asked by: Curtis H

Expert Reply:

Since the left turn/brake lights are not working on two different trailers, the common denominator is the truck. To determine if it is the truck wiring or just a fluke with both trailers, you will need to test the truck side connector using a circuit tester such as # PTW2992.

Have someone sit in the truck and apply the brakes and then left turn signal while you test with the circuit tester. If there is no power at the connector for these functions then that indicates a problem with the truck wiring. The place that checked it out the first time should be the ones to fix it.

It is possible that there is still a fuse blown or missing or a relay that is not working. Use the owners manual to find fuse and relay locations. The best way to test a relay is to use a known good one in place of a potential bad one. If the function starts working then you know what the problem was.

If everything checks out on the truck then it must be the 2 trailers. Likely causes include a dirty or corroded trailer connector, bad or weak ground at the main trailer connector or left side tail light. Or if a plastic license plate holder was added between a light ground and the trailer frame, the trailer has a tilt bed, aluminum frame, or folding tongue, any of those can interrupt the ground.

expert reply by: Michael H