Ok, I know this topic has been picked to death on the forums, but I'm new and I haven't been able to find a definite answer. I have a 97 Chevy Blazer that I just picked up and the 3rd brake light is out. I've checked the fuse box for the CHMSL fuse which is tied into to other lights - the fuse is good. The owners manual says this fuse also controls the CHMSL Relay. I haven't been able to find a location for this relay on a 97 model. Does anybody know where it's at? I know there are 3 relays on the firewall of the passenger side under the hood and 3 relays behind the glove box. Any help would be great.

 

To my knowledge the 3rd brake light should not have a relay, since on blazers brake/signal are ran through the same wire, the 3rd brake light ties into near the brake light switch. To prevent it from flashing when the signal is turned on.

 

I'm confused just because in the owner's manual it says that one fuse controls the Stoplamps, Hazard Lamps, Chime, Center High-Mounted Stoplamp Relay, Center High-Mounted Stoplamp.

 

hmmmmmm. gave it a google search and came up with this, let me know if it helps
Third Brake Light (CHMSL) Problem - S-10 Forum

 

I read your post and decided to check if I had voltage at the brake light connector in above the rear dome light. Once I managed to wedge the brake pedal down I was reading 11V without the truck running. So I'm now assuming the LED brake light is shot.