Could use some help diagnosing a problem. My brake lights won't work, although the same bulbs come on with turn signals and hazards. Center brake light also works. Checked stop lamp fuse and that is okay. This is a 2004 Trailblazer. Thanks!

 

The brake light and the turn signals / hazards use different bulbs in the back of the GMT360 trucks.

Do you have power to the stop lamp pin in the trailer plug?

 

Not sure what the pin is, how do I check this?

 

Google '7 pin trailer pinout' and you will find the answer...

Use a test light to test for power.

 

I didn't have a test lamp, so I hooked up to the trailer and the Brake lights work. Does that answer your question? If not do I just touch the test lamp to the stop light pin?

 

Sorry, no that doesn't actually help... I read the schematic too quickly and mis-read it. The trailer brake lights are just an interrupted turn signal.

If your VEH STOP fuse (#34 15A) located under the driver side rear seat is not blown, then the next step would be to check the wiring back at the tail light housings themselves. You need to check for +12V at Pin A of the tail lamp circuit board wiring connector.

 

The fuse is good. I will look into the tail light housings. Is it possibly the brake switch even if the center brake light works?

 

As the schematic shows, the brake switch provides power to the CHMSL, the lower brake lamps, as well as the trailer brake lamp circuit so the switch itself is working.