start with a motor test of the genny, thenmove to a full field test.
and to dothat.. you need to determine if A circuit or B circuit.
look at the bottom of the reg. if there is 1 bias resistor and it is between the field tab and the ground tab/case.. it is likely A circuit.
if there are 1 or 2 or more bias resistros... and one is from field to armature.. it is likely B circuit.
to motor test A ckt, slip belt off.. remove feild wire.. jump field on genny to ground, jump bat hot to armature. if she takes off spinning.. genny is PROBABLY ok..
to motor a B circuit, slip belt off, remove field wire. jump bat hot to field AND armature.
if it spins, it is PROBABLY good.