Brake Lights don't work but the third light does

I have an 2005 GMC Envoy and the brake lights have quit working but the third brake light does. I have checked the fuses,bulbs, and have replaced the brake light switch located on the brake pedal.

Test for current at the brake light bulb sockets as someone steps on the brake pedal. You may have a wiring issue.

Check fuse 34. It looks like if that fuse isburned out, that would still let the third brake light work. I attached the wiring diagram so you can see what I’m talking about. Otherwise if everything else you’re telling me is exactly how it is, then you’re looking at bad light sockets or bulbs or connector somewhere or wiring. The wiring does go to the multi-function switch, but it looks like there is nothing in there that would cause your problem. Few more thoughts. If your cruise control disengages when you tap on your brakes, you know your brake switch works. What happens when you turn on your emergency flashers? Do your brake lights flash on and off like they are supposed to?

Are these the type of bulbs with the exposed wire for a contact? if yes these are problematic and the issues could be in the socket, we replaced many of these bulb/socket combos on many GM products and BMW products.

Thanks for the wiring diagram. I will check the fuse again. I am pretty sure I looked and swaped #34. Also I checked the emergency flashers and they work fine. I did not think about testing the cruise control before replacing the brake light switch. Somebody also told me there could be a switch or someting in the steering colume that could caus this. Have you ever heard of this?
Thanks for the reply

Yes these are that type of bulbs. But if they are bad sockets should boths sides go out at the same time or does one side going bad effect the other side due to the way they are wired or something?
Thanks for the reply.

They are used an equal amount, can you see any issue on the exposed bulb wire?

The stop lamp switch does go to the multi function switch (blinker switch), but I don’t know how it’s wired internally, and doubt it’s keeping your brake lights from working. However since the problem persists, if you can get to your blinker switch, you might try to spray a little contact cleaner or wd-40 inside the switch and work the switch through all modes. Some of them are pretty well sealed up. I doubt you have two bad bulb sockets at the same time. It could happen. That’s what’s fun about troubleshooting electrical problems, you can never say “always happens” or “never happens” to any situation. About the time you do, someone or something will prove you wrong. IT might be time to pull out your VOM and start pulling connectors and checking for voltage. Hey call me if you want and I’ll walk you through the wiring diagram…8015406057…

Fuse 34 may be ok but you need to check for power getting to the fuse when the brake pedal is pushed and the brake switch is closed. Use a test light probe to verify the power. If you have power to that point then there is a break in the wire to the lights after the fuse.

If it was a bad brake light switch your 3rd light would not work because there would be no current past the switch.You have a break in the wiring or a bad connection.