Remove the field wires and the armature wires from the generator. Cover the ends of the wires with electrical tape to prevent damage.
Attach a jumper cable from the generator field post to an airframe ground.
Attach a DC voltmeter to the armature terminal of the generator. The plus side of the meter connects to the field post and the negative side connects to the ground.
Watch the voltage as the throttle increases. The faster the generator field, the more energy output. If the voltage does not increase, then you need to check if the engine needs to be polarized. Your generator may also be faulty.