I don't understand how you read zero on your coil but let's leave that one. I hope that your test meter is OK. With the motor running, if you place a very temporary ground on the field at the generator, that should cause the A terminal on the generator to rise in voltage. That would indicate that the generator may be OK. You don't want to leave the ground on very long because on a healthy unloaded generator, the voltage can go to 20 volts.
