Take your tail light assemblies off and jam something on the brake pedal to power up the brake lights. Run a meter over the backs of the tail light plugs to check if there's any voltage present. This will eliminate if the globe bayonets are corroded and causing a dead circuit. If it's dead at the plugs then move up the brake light wiring loom and keep checking connections until you find live power. This will indicate what point the wiring has failed. Also, check your earth/ground leads. They are a major culprit of gremlins in your electrical system. Unplug/remove bolts and give the eye connectors and terminals a good clean. Good hunting