dead battery

67 barracuda. 400 727
started fine. Drove to job site.

Went to start it at end of day and it hesitated but started.
Turn lights on and they flicker badly. I push on the headlight switch sideways and the lights turn off. They flicker back and forth when messing with the switch. Running lights and blinkers working. NO headlights.
Proceed to drive it home in the dark with just halo's showing. Couple blocks from my home is a high school foot ball game. Cop in front of high school so I pull into the car wash. Kill motor and wait for a chase vehicle. Then the car won't start again. Jump it and have no lights but have running lights.
Now it's just dead. Gel battery. No burned wires anywhere.
Opinions of what I need to check first? I would assume the alternator but it is basically new with only a few hundred miles on it. Could the headlight switch cause this?