Field Coil Draw

Connect a wire between one field terminal of alternator and negative terminal of a fully charged battery. Connect test ammeter positive lead to battery positive 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 coil). A higher rotor coil draw indicates possible shorted rotor coil or grounded rotor. No reading indicates an open rotor or defective brushes.