An f or fie indicates the field terminal.
Old ford voltage regulator wiring.
Connect the field wire field coil wire to the field terminal on the regulator.
The corresponding terminal for the generator alternator wire is marked an a or g sometimes arm or gen.
One way to wire a 3g alternator in place of the old 1g setup is to simply splice the old external regulator s i and a terminal wires into the corresponding wires from a 3g connector pigtail.