Unless you insulate the brushes from the armature commutator, the ohmmeter will indicate a short. There should not be a circuit from the commutator to the armature core, but one of the brushes is grounded. The other brush is connected to the ARM terminal and the circuit tester will show a clear path to ground even on a good generator. That's why it's necessary to have a cutout relay on a DC generator system. Fix the broken wire, and you should be good to go!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!