There MAY be a body connector somewhere on the firewall that has the rear lighting harness running to/from it. I'd check and see. If so, it is the best place to check the condition of the entire rear harness. Also there is a big connector that connects the turn signal assy to the harness. Find the dark green wire on the left hand and check there. The light green going to the rear is the back-up lights. The Right turn/brake is the dark green one, and the left is yellow. All other rear lights are on the brown lead. It goes without saying to double check your grounds to the frame!
best wishes,
Les
