Headlight switch.

I would guess not all years had the ground wire on the switch. The switch had to be grounded, even through the dash, for the dome lamp to work "on the knob."

Headlight switches fit a million models for years and years.

Tail/ park and head battery power comes from two sources.

Headlights only power comes off the black wire splice in the ammeter wire "welded splice" not fused, direct to B1 terminal on the switch.

Tail, park, and dimmer controlled dash lamps comes to B2 from the fuse panel. Additionally, after the dash lamp power leaves the dimmer, that power then goes to the small INST fuse in the fuse box, where its' fed out on orange wiring

Do hazard and brake lights work?

Brake lights come from the fuse panel "hot buss" from a fuse, fed to the TS switch, so they should work all the time.

Hazards work? They are fed from a hot fuse through the separate flasher, so they also should work, regardless of key position.

I would check for power at B1 and B2, then move to the dimmer switch and see if it's there. AFter that it could well be a mismatch of harness parts, or just plain poor connections in the bulkhead connector