1998 GMC C1500 No Brake Lights

do you have parking lights

Yes. I have parking lights, turn signals, reverse lights.

Hello
tools needed for the test a simple test light and or volt meter locate the brake light switch on top the brake paddle check for power at one of the two wires do you have battery power ?if not problem is no supply volts (org wire)check fuse #1 inside the truck fuse panel if 4way flasher work but no power to the brake switch check the wire most common when installing an alarm system or remote starter they cut them wires .check them check fuses and wiring on the circuit if yes and u have power step on brakes u should have power on the other wires if not recheck the switch and its adjustment check if 3rd brake light on and if so suspect the multifunction switch.

ok now this may sound stupid but check the bulbs make sure they are 1157 bulbs and put in the wright way I have found this to be the case on alot of chevys