Field Coil Draw

Connect a wire between one field terminal of alternator and positive terminal of a fully charged battery. Connect test ammeter positive lead to the other field terminal of alternator and negative lead to battery negative terminal. Slowly rotate alternator rotor by hand. Observe ammeter reading. Field coil draw should be 4.75-6.0 amps. (100 amp.) or 4.5-6.5 amps. (all others) at 12 volts. A low coil draw is an indication of high resistance in field coil circuit (brushes, slip ring, or rotor). A higher coil draw indicates possible shorted rotor coil or grounded rotor. No reading indicates an open rotor or defective brushes.