1999 Chevy Silverado - 3rd Brake Light Inop

third brake light problem ' Chevy Silverado and GMC Sierra Forum (silveradosierra.com)
Separate fuse for 3rd brake lite check link above.

For starters it is spelled "Brake" light...LOL . Sounbds like you may have a brake light switch that has gone out. In yor owners manual does it show more than one fuse for the brake lights? Most vehicles with a thrid/highmount brake light split the brake light power to either the left and third brake light and the right brake light or vice versa, or posibble 3rd brake light on its own fuse. I would check if all of the brake light including the 3rd brake light dont work. If no lights work at all it leans toward the switch which controls all or them to activate hence the brake light switch. It should be mounted on your brake peal arm or to the main base. The pedal lever activate the switch when you depress the brake pedal.

Have you checked the brake light switch by the brake pedal?

I had the same issue. Check fuse number nine.

Hi, the likely problem is your VEH STOP fuse. in the engine compartment fuse box. Please let me know if you have questions and thanks for using FixYa.

I've worked on these the first drove me crazy. its the turn signal switch every thing runs thru these. head lights, turn signal, brakes. except the third brake light. it runs directly from the brake switch. go figuare

On either end of the 3rd brake light housing, there will be a screw. Just remove these screws and the housing will slide right out. Then you can just pop the bulb out

think brake switcjh it is a dule part switch.. if bulb good then switch next culprit

check all your wiring from the light to the fuse panal. that should fix it

check grounds on rear light assy's