ok read about 90% of the no brake light threads
mine was the same symptoms, no lower brake lights, 3rd one works, the hazard switch got replaced (i hate inverted torx btw), still no lower brake lights AND lost my flashers, replaced flasher and no change. tweaked the hazard switch and got some response but still no flashing or brake lights. I have tail lights with headlights/running lights, but still no brake lower brake lights or flashing on any turn signal outside or inside.

did I say I love Blazers & coffee? COOL cause right now I'm only enjoying 1 of them.

 

Probably missed something...ya know? like details of my ride?
2000 Blazer LS 2dr 4x4

 

I had one brake light that didnt work but the tail light did and it ended up being the turn signal lever.

 

How did you diagnose?
How did you figure that out?

 

I read a post off the forums about it. Try to jiggle the turn signal handle and watch the brake lights and turn signals, this is how I found mine. Do a forum search, there are a few topics

 

Get under the back of your truck and clean your ground wires

 

Checked, cleaned, checked again. No change
Need more coffee

 

I have a 2003 Blazer 2 door LS and the right rear brake light was out. I replaced the 'multi function switch' aka the turn signal switch and the switch on the brake pedal. Both painful jobs. I then found out it was the fuse in the underhood panel, IIRC. Check all the fuses and replace any that look suspicious. I violated my own motto. Do the easy fixes first.

 

After replacing the hazard switch, I replaced the flasher.
Then checked the grounds. Tweaked the hazard switch quite a bit.
Then checked the threads again, checked and replaced fuses and relays.
Said more than a few 4 letter words, threw my 9/16 combo wrench.
Read the threads AGAIN. Replaced the turn/combo switch and all my lights work as designed.
Btw had a couple pots of coffee through this whole thing.
The 9/16 wrench leaves a good hole in the trashed storage door too.

 

Welcome to the Blazer Skinned Knuckles Club. I am glad you got it fixed. Now tell me why my 'airbag' dash lamp is always on. Thanks!