Confused on wiring. 1964 Barracuda.

67Dart273 said
Yes the adjustment is for dash lights but there is a separate switch contact, when twisted ALL the way left (and there usually is a detent) the contact grounds the yellow buss, for the dome/ courtesy

Yeah the rotating part hits what appears much like a light switch in a wall of a home. Inside the switch are the contacts that turn the dome lamp on.