2003 Crown Victoria - Brand X 408A HO alternator - P0622 & battery light, but charging at 14.75V

Looking for advice from anyone familiar with Ford charging systems or high-output alternators.
Vehicle:
2003 Ford Crown Victoria
Brand X custom-built 408A peak / 213A idle alternator
Stock wiring (Big 3 not done yet)
New alternator connector installed during the swap
Symptoms:
Battery light is OFF immediately after startup.
About a minute later, the battery light comes on.
Charging voltage remains around 14.75V at idle.
Battery is 12.8V with the engine off.
Alternator appears to be charging normally.
Codes:
P0622 – Generator Field (“F”) Control Circuit.
The alternator is producing voltage, so this doesn’t seem like a “no charge” issue. I’m wondering if this is:
A grounding issue due to the original 2003 wiring.
A problem in the field/control circuit.
A regulator compatibility issue with the PCM.
Something else I’m overlooking.
My next step is doing the Big 3 (including engine block to chassis), checking all grounds, inspecting the alternator connector and wiring, then clearing the code.
Has anyone run into P0622 after installing a high-output alternator on a Panther platform? If so, what ended up being the cause?

This is indeed AI generated summary I’m in a massive rush tryna get shit done rn leave me alone about it please.