Trailer brakes light do not work

DECLANOSHAUNESSY

MEMBER
2004 CHEVROLET TRAILBLAZER
4.2L
6 CYL
2WD
AUTOMATIC
207,000 MILES

All lights on the car work fine. When the trailer is attached; running lights work, turn signals work but when the brake pedal is depressed the lights turn off. The car lights are still working but not the trailer. The only change I have made recently is a new brake pedal switch.

All fuses have been checked on both panels.

Suggestions? The brake pedal switch was very inexpensive and I may replace it to check.

3 Replies

STEVE W.

MECHANIC
13,024 POSTS

Welcome to 2CarPros. Okay, I read this as the trucks lights work fine. Then you connect the trailer and the trailer and truck lights work until you step on the brakes? Then the trailer lights all stop working? Is that correct? Has this trailer worked properly with the truck before? Is this the factory trailer harness or an add on? Is the trailer equipped with a 4, 6, 7 pin connector? The description sounds like a bad ground between the trailer and truck. A quick trick to test this would be to use a jumper wire on a bare spot of steel on the truck and another on the trailer. If the lights now work you need to see if it's the ground wire on the truck side or the trailer side. I've seen more than once the issue was a bad connection in the plug itself. Could you take pictures of both sides of the connectors and post them here?
As the lights work on the truck with the trailer disconnected I doubt the switch it the problem.