Depending on the vehicle, the brake light is either a separate bulb or a single bulb with two elements in it. A power surge could blow all three bulbs, but a bad brake switch is more likely. Could be a fuse also. The brake swith is at the top of the arm that the brake pedal is on. You can jump across the two wires on the switch and the lights should come on. If they don't, it is most likely a fuse.
blubs blown? Check the turn signal switch.
Depending on the year, there may be one fuse for all three brake lights, or two fuses, one for the highmount brake light and one fuse for the two lower brake lights/tail lights. So, if all three brake lights are out, it could be just one fuse or perhaps the brake light switch which is on the brake pedal metal arm assembly.
It probably indicates that both your other brake lights are burned out and need replacing. BTW: It is illegal in most (if not all) jurisdictions to drive this way.
A third brake light is used to provide a deceleration warning to vehicles that can't see the left and right lights. You can learn more about these brake lights at the Wikipedia.
Fuse for the "Third" Brake LightAlthough I have no experience with the Chevy Tahoe, the systems are similar for almost all vehicles.The third brake light is tied into the wiring for the other brake lights and is protected by the SAME fuse they are.Thus, there is no separate fuse for the third brake light.Therefore, IF your other brake lights are working, then a failure of the third brake light to activate IS NOT caused by a fuse, but instead an "open circuit" condition in the "dedicated" third brakelight wiring [from where its wire "splits" off of the wiring harness to the other brake lights].This is usually caused by a connector which has become disconnected, or a cut or broken wire.
The third brake light is named for then Secretary of Transportation Elizabeth Dole and are called "dole lights".
Probably the bulbs are burned out, or the sockets that hold them are not properly seated causing a grounding problem. FriPilot
New bulb needed or broken wire
this tells you is a simple wiring problem.most likely a loose wire from the third light to the other lights.(third lights provides the power to the other lights)
either dimmer switch or blown fuse If you are saying that the tail brake lights are working but the third brake light is not....It may be a defective turn signal switch in the steering column.
wrong bulbs or bad earth
Chevelles never had a third brake light since the Chevelle name was dropped after 1977. However, third brake lights were first installed (and required) in 1986.