[Caldon]

FWIW, just to follow up, in trouble shooting the loss of both brake lights and turn signals, it seems that the original (?) wiring passes very close to the engine/exhaust and had finally "melted". So re-wiring using a "better" routing fixed both the brake/turn signal lighting problem AND the gas gauge "pegging full" problem when the light switch is turned on. Voila, functioning as it should. Thanks again to all helpful comments.