Trailer Lights Stop Working When Headlights are Turned On with a 2007 Chevrolet Avalanche

Question:

Ive installed a 4 pole wiring harness on my trailer and connected to my 07 Chevy Avalanche via a 7-to-4 pole adapter. The lights work fine during the day, but they wont work at night. If I turn off the light on my Chevy, the trailer lights will work. Can you help me figure this out? Thanks.

asked by: Jorge P

Expert Reply:

The most likely cause of your problem is a bad ground connection. It has enough of a connection that it works in the day time because you have less current draw on those circuits with the head lights off. As soon as the headlights are on, you are pulling more current than the weak ground can support.

Check the ground connections on the trailer wiring. Make sure you have good metal to metal contact. Paint and corrosion can act as insulators so make sure the grounds are touching clean metal. Check the grounds of the lights themselves as well as the ground wire that goes to the 4-Way trailer connector.

Finally, check the vehicle. Trace the ground wire from the 7-Way and make sure it has good contact with the Avalanche frame. Again, check for corrosion and clean it up if you find some.

expert reply by: Patrick B