Headlight switch problems?? 69 dart.

Sounds to me like that switch is AFU

Here is how they work:

B1 gets main power AND THIS IS NOT FUSED from the ammeter circuit. This powers ONLY the headlights, nothing else. There is a breaker in/ on the switch for the headlight circuit

B2 powers the rest, park, tail, and dash

The unconnected terminal is for park lights in later years, and this causes the park lamps to be on with headlights

The park circuit internally feeds the dimmer control. That power goes through the dash dimmer and OUT on the TAN wire to the inst. fuse in the fuse panel, then from there, feeds all dash lamps on orange wiring.

So for dash lamps to work, the B2 must be getting power and the park/ tail circuit working. The dimmer must be twisted somewhat left, and the inst. fuse must be good.