Use a factory service manual wiring schematic before any of the ones on mymopar.

You could easily check all the circuits by hot wiring the plug. Maybe use a fused jumper to test.

Could be a bad switch.

If it's not a 100 point show car, put a good headlight relay kit on it. The owner won't regret it!

A 71 with one of my kits installed, before and after on low beam.