Re: dim headlights
If lights are dim, no point in doing any thinking/asking/guessing at all. Check battery voltage with everything (including engine) off, with engine running at 2,000 RPM with everything off. Then do it again with high beams on with everything else off (including engine), then with as much stuff on as you can with engine at 2,000, High Beams, brake lights, fan at high...
List those 4 voltages, should only take 2 minutes to test.
rough estimates of them should be 12.6, 14.3, 12.2, 13.9 something like that. Basically over 13.8 when running, and under 13 when off, but always over 12 (unless cranking).
Also, how old are the bulbs, they don't get brighter after 50 years...
1967 El Camino Malibu - Deepwater Blue
ZZ4 350, FiTech 600 complete!,Roadmaster tank, 700R4, Underdash A/C in progress, JGC Steering, 1990s truck serpentine.