Engine stays running without key in ignition (and more!)
This post shows how the isolated field alternator works with its regulator.
Identifying Chrysler Alternators (1960-1976)
Because the regulator has boot type connector, voltage it is sensing will have to be the next closest locations in the J2 circuit.
Voltage of the J2 circuit should be fairly close to the votlage measured at the alternator output and the battery at hte same time.
If there is a big difference, then that indicates resistance to current flow.