Did I misunderstand? I thought you said you had to cut ALL wires, that is, the main battery wire? to stop it charging. This sounds more like how a "one wire" with integral regulator would act
Here's the thing...........if a typical isolated field unit is charging out of control, one which uses an external regulator, you should be able to disconnect EITHER field wire to stop it charging.
If you did that, and it continues to charge, then the regulator is NOT the cause.
The problem for me is I don't have documentation on any of this "new" stuff.
Your diagram is not proof that the regulator "was" in the PCM
