Trailer brakes light do not work

Tiny
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.
Tuesday, October 29th, 2019 AT 7:57 AM

3 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,414 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.
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Saturday, February 27th, 2021 AT 12:34 PM
Tiny
DECLANOSHAUNESSY
  • MEMBER
  • 2 POSTS
Thank you Steve. The connector is from the factory and it is a round connector (7 pin) to an adapter for a 4 pin. I will check the ground.
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Saturday, February 27th, 2021 AT 12:34 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,414 POSTS
I would start at the truck connector, the wiring is in the image.
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Saturday, February 27th, 2021 AT 12:34 PM

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