71 duster headlight issue

The light switch has TWO power sources, one for tail/ park/ dash, and the other is UNFUSED from the ammeter circuit and supplys ONLY the headlamps

There is a CIRCUIT BREAKER built into /onto the light switch

If the breaker gets weak, or if the connector is loose and the terminals get hot, it will cycle on/ off. This can also happen with "too large" lamps.

Investigate going to a pair of relays--one for high, one for low. Crackedback, member here, sells a nice setup for this