Alternator or VR issue?

DH-66cuda said
this is a little beyond me.

It should make more sense when you understand the alternator operation.
I think the most succinct explanation I've done is in the sticky.
Pay most attention to the Grounded Brush Alternator in post 1 and 5.
https://www.forabodiesonly.com/mopar/threads/identifying-chrysler-alternators-1960-1976.475691/
The VR diagrams above and a full explanation can be found in the 1966 Chrysler Master Technicians Conference #11.
Available online here: Browse MTSC by Model Year – 1966 – MyMopar
There's also a filnstrip video.