Field Coil Draw

Connect a jumper wire between one field terminal of alternator and negative terminal of a fully charged battery. Connect ammeter positive lead to the other field terminal of alternator, with ammeter negative lead contacting battery positive terminal.
Connect a jumper wire from negative terminal of battery to end shield. See Fig 1. Slowly rotate alternator by hand. Observe ammeter reading. Field coil draw should be 4.75-6.0 amps, for 117 amp. alternator or 4.5-6.5 amps, for other models at 12 volts.
A low coil draw is an indication of high resistance in field coil (brushes, slip rings or rotor). A higher coil draw indicates possible shorted rotor coil or grounded rotor. No reading indicates an open rotor or defective brushes.

Fig 1: Ammeter Connections for Field Coil Current Draw Test

Courtesy of CHRYSLER GROUP, LLC