welcome to Team Camaro midlife, it could be a vacuum leak in any of the hoses and or connectors from the headlight switch, to the vac. canister to the vac. modulators down under the fenders.
Best way to learn all possible answers is to use the 'search' feature at the top of the screen, type in 'rs headlights' or 'vacuum modulator' or other words that might be found and you will find tons of links to that topic being discussed in length here. Read away.
Also if dont have one, buy the 69 Assembly Instruction Manual that has complete cut away diagrams of all featurs of your car to help guide you along.
You will enjoy this board and learn alot from some very good and honest experts that live here.
69RS 350/255 LM1, Balanced, TRW forged pistons, .30 over, TH-350 auto.,
Dover White,Blue Vinyl top, F&R spoilers,pdb, close ratio ps,am/fm,3.08 Posi., A/C, fold down rear seat
My RS www.brainerd.net/~knudsen/69RS