On a Three Phase transformer supplying my local housing estate
the star point is both the earth and neutral.
Thus on the U.K. systems phase to phase is 420 to 440 volt and
phase to neutral is 240 to 250 volts.
This is all standard Three Phase Technology.
However this AUX terminal on Prestolite Alternators when the system is d.c. airframe return is a total unknown.
I suppose the next move is to try e/mailing Prestolite.
Regards