What to Check if Only the Running Lights are Working on a Trailer

Published 07/22/2021

Question:

2009 silverado wt with factory 7 prong plug. the only trailer lights that work is the runnning light. I have checked the plug itself for continuity on each prung and i have checked for power at the harness end for 12v for each connector. again no power but running light. all fuses inside and under hood test good. any other ideas? thanks

asked by: Paul

Expert Reply:

If your towing fuses are all good, it is most likely the plug itself that has gone bad.

I suggest testing the wires at the back of your plug to see if there is power going to the plug. If you do have power going up to the plug, you will need to replace the # HM40975.

If you do not have power, you have a break in the wires somewhere. You will need to either trace the wires to see where the break is, or take the vehicle to an auto shop to have fixed.

expert reply by: Lazer S