I checked voltage across the battery with the car off; it was 12.57 volts. With the car running voltage measured 12.3 volts, so something is wrong.
I need to know how to isolate the generator voltage in order to check its output. This is a Ford generator, the wiring to the 3 terminal voltage regulator is attached (B, F, and A terminals).
Most posts for this online are for a different type of generator. My generator has been rebuilt 3 weeks ago and I replaced the voltage regulator at the same time (repo from NPD). All wires look good and the harness is new.