I have a 1997 Blazer. The 3rd brake light has never worked since I bought it a few months ago.
Yesterday I went and bought a new one. Installed and nothing. Grabbed the test light and had someone push the brake pedal and tested for power at the yellow wire and the black wire and nothing.
Thinking maybe it was a fuse, the problem there is, there is no such thing in the fuze box for the 3rd brake light.
No fuse box in the engine bay either, not that I could find anyway.
Is there a relay that could be causing this? If so where?

 

Should tie in with the regular brake light fuse.

I would inspect the wiring for any shorts or bad connections. Trace it back if you have too.

 

Here ya go, this should help.
https://blazerforum.com/forum/2nd-ge...-solved-25868/

 

Not sure that will actually help. The CHMSL (center high-mounted stop light) relay is in the under-hood fuse box on 98+ vehicles; but 95-97 don't have an under-hood fuse box. They have three relays in the glove box; but none of them is the CHMSL relay.

It's actually a bit of a mystery and I wouldn't mind the answer myself, before I drop the cash for a new light strip (mine isn't working either). Everything I can find suggests that 95-97 has a CHMSL relay...my 95 owner's manual explicitly says that fuse #1 (STOP/HAZ) in the dash block feeds the "CHMSL relay" among other things - but I'll be darned if I can find anything anywhere whatsoever that actually says where the relay is. I wish I had a wiring diagram.

 

Thanks for all who have replied. I spent a few hours yesterday trying to find a fuse, relay anything. But gave up.

Now I am wondering if I can wire it to my brake lights? Not sure if brake and turn signals use the same wiring either.

Also is the wiring at the brake lights Yellow/Black like it is on the 3rd brake light?

Where is the 3rd brake light getting power from anyway?

 

You cant just tap into the brake lights for the 3rd brake light, or it will flash when you turn on the blinker.
You can however, run a wire all the way up to the front and tap into just after the brake light switch under the dash, and ground it somewhere in the back. That is what I did when I put a 3rd brake light on my truck.

 

Where would I find the Brake light switch under the dash?

After further inspecting, someone else has been poking around, literally. I seen a couple tiny holes someone did to test for current on the yellow wire at the 3rd brake light. Which has me believing they gave up.

Also searching a few threads on here, I came across this one How To: Wire RHD Euro Blazer Tails - DISCUSSION THREAD - Blazer Forum - Chevy Blazer Forums and it shows kind of what I am trying to do. Except with regular Blazer tail lights. Just curious if he got his to work by changing the wiring? Is this why it will flash if I use the turn signals because I believe he went off the front turn signals for the rear?

What is puzzling me is where is the relay? Would there not have to be one if the turn signals and rear brake lights run off the same wiring then?

I still don't see how the brake light and turn signals share the same wiring.

Please forgive me. All I know is old German wiring from Air-Cooled VW's where brown is ground and Black is hot. This is also my first water pumper vehicle.

 

I am still trying to figure this out. Any help is appreciative.

 

just tap into the brake light switch under the dash, its attached to the brake pedal, should be white, and have 2 wires coming off of it. probe and find which wire does not have power when the brake pedal is not pushed, but does when pushed, splice into that, run the wire back and you are good to go. with the addition of grounding it of course, but that is fairly easy, can just clean some metal back there under an interior panel and use a self tapping screw or bolt.

 

iian, are you testing for current by putting a probe in the wire and the other to a ground, because if so this is how you would test for voltage (in parallel). Sorry if you are doing it correctly, it just seems by the way you wrote your message that you are testing for current in parallel. Current needs to be in series with circuit. If so try checking the voltage to see if you are getting a voltage drop.

I had an issue with my 3rd light and replacing it seemed to do the trick because I was getting voltage to the light, but it wasn't turning on when I stepped on the brake.

best of luck trying to figure it out, electrical stuff can be a pain sometimes.