The Advance-Design light switches provided power for a variety of circuits.
There was a dome circuit and separate rheostat controlled "dimmed" circuit (among other circuits). The dome circuit was not rheostat controlled and, as indicated above, it was always hot (even if other lights were not on).
The dash bulbs were connected to the rheostat-controlled circuit (instrument and ignition lock light in the diagram/photo - dash/instrument circuit); and, depending on the installer's choice, the radio, lighter, and clock bulbs (if those accessories were used) were usually connected to the rheostat controlled circuit but they might have been connected to a another "night-light" circuit (with no rheostat control - maybe the tail lamp circuit?).
Grounds in most (all?) A-D lighting circuits were provided through the socket-housing and lamp-housing, ultimately to the frame (which was strapped to the ground lead on the battery).