I had this happen to mine, I couldn't figure it out. everything seemed fine. I finally narrowed it down to the switch. Its the whole assembly in the steering column. Once I replaced it ( about 2 hours work) everything works fine. If you need more info louiekempton@horizonview.net
It is important to have working brake lights on a vehicle. If the brake lights are not working a person should first check the fuse, bulbs and at last the wiring.
either your fuse is blown or the wiring is bad
the connection between the battery and the brake lights
Check the brake light switch.
BEHIND THE BRAKE PEDAL
If the brake lights do not work on Chevy Venture van 2000, try to disconnect the brake switch. Then short the two contacts of the connector to check if the brake lights are now working.
turn signal switch needs replaced!
Check the fuse, check the bulbs and check the brake light switch, it should be one of those.
The 2001 Chevy Blazer brake lights may not work and the third bake stays on because the current light needs to be replaced. A replacement brake light can be purchased at an Auto Parts store like Pep Boys.
Check the fuse, check the bulbs and check the brake light switch, in that order.
The center high mount led brake light unit has been known to go bad.
I assume you have checked/replaced the bulbs. Take a cicuit tester and check the wire harness connections under the bumper and around the trailer connector if you have one. The problem must be at that area IF all your other lights are working as you said.