Brake light not working

Have you checked voltage and ground that apply to that system? You can use a test light. Did you check the stop/hazard fuse? Not only check the fuse, use a test light and check voltage on fuse circuit. Did you check the stop lamp switch? Activated by brake pedal arm, check voltage to and from switch for brake lamps, white wire should be voltage to stop switch. When switch is activated, orange wire carries voltage from stop switch for stop lamps. Voltage to lower stop lamps is usually wired through the multifunction switch. At the rear lamp, stop and turn use the same bulb filament, just not at the same time. At the rear lamp, if three wires, brown wire is voltage for tail lamps, the black wire is ground. The other color wire is voltage for stop and turn. I can only help with testing. You have to do the actual testing, with test light.