The third brake light is not working?

JULIO MARIN

MEMBER
2008 CHEVROLET SILVERADO
4.3L
V6
2WD
AUTOMATIC
133,500 MILES

So, for some reason my third brake light is not working at all. I’ve tried replacing the light bulbs and that didn’t fix the problem. And I checked for a blown fuse, and they all seem to be working fine. I'm not sure what to do next to fix the problem.

4 Replies

KEN L

MASTER CERTIFIED MECHANIC
47,639 POSTS

The third brake light is on its own circuit, when the brake pedal is down do you have power at fuse CHMSL under the hood, there is also a CHMSL relay in the same place. I would swap out if you are not getting power. If you are getting power, I would check the lighting ground. This guide will show you how and I have included the third brake light wiring diagrams so you can see how the system works.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

This guide may help as well:

https://www.2carpros.com/articles/brake-lights-not-working

Here is the location of the CHMSL fuse and CHMSL PBC relay under the hood. Check out the images (below). Please upload pictures or videos in your response to the problem so we can see what's going on.

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Wednesday, January 24th, 2024 AT 1:12 PM

JULIO MARIN

MEMBER
8 POSTS

Okay, so I put the test light on the fuse, 49 and the test light did not go on I checked the fuse, and it seems okay. I checked other fuses, and they all seemed to be working, except the three fuses that are next to fuse 49 which is 44, 55 and 56. They don’t light up either when I put the test light on them.

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Wednesday, January 24th, 2024 AT 2:50 PM

KEN L