The "Stop/Haz" 20 amp fuse which is hot all the time supplies power to the brake lights through the "Stop Light Switch" and then to the "Directional Signal / Hazard Warning Switch Assembly" (mtg on steering column). Shop manual says to check connector C124, located under LH instrument panel, near the fuse panel. Having power there, check for voltage / test light from the center contact of one stop light sockets (bulb removed), to the ground at the rear left bumper cylinder just aft of the radio antenna. If you read voltage on a meter and get a lit test light, with helper pressing the brake peddle. No light tells you the problem is between there and C124. If you get a light, Re-insert the stop lamp, still no light in socket, check for bad ground or damaged wiring at the socket. If you get no voltage / light, then you will need to check the body wiring harness, book shows it is locate above the gas tank. Before you get to deep in taking things aparts, double check all connection points for damage or degraded wiring, or if you have worked on someelse under the dash panel recheck all connections first.
One hint; a test light with 3 - 4 foot leads with clip on the ground side helps to insure a good ground connection at a good frame ground point and frees up one hand. I use a home made test light with very 4' long leads.
Hope some of this helps.
