'76 Camaro turn signal problems.

Currently having a problem regarding the driver-side turn signal of a 1976 Camaro. As it now stands, only one of two filaments is receiving power. With parking/headlights off, the turn signal works as intended, though dim with a single filament. Turning on the parking/headlights causes the gauge cluster (wired correctly, already checked) to show constant power to the driver turn signal, but the filaments do not light up, nor does attempting to use the left-hand turn signal work. Turning on hazards causes only one filament to light up, the same one that works without parking lights on, and it flashes opposite of the right side signal, which works as intended with both filaments lighting up. Any help or ideas as to the cause and solution are greatly appreciated.

Thanks!

Check/clean the ground for the lamp housing and socket.

Seconded, check the quality of your grounds.

Obviously an old thread, don't know how I missed it. Hopefully the O.P. found and corrected the cause of his problem, (which is often dirty or missing ground connections), as Blue Bowtie and Silicon 212 suggested.
For future reference, folks that may run into this issue - My son's car had the exact same problem, and we cleaned the sockets, ground connections, replaced all the bulbs, checked the wiring to the lamps... Wound up eventually replacing the turn signal switch assembly within the steering column. The replacement unit was from Classic Chevy Parts in Oklahoma City. Included the harness, and was a very well made reproduction part. Solved the problem for us.