Field Coil Draw Test
- Connect jumper wire between field terminal of alternator and negative terminal of a fully charged battery. Connect test ammeter positive lead to other field terminal of alternator and negative lead to battery positive terminal.
- With alternator on an insulated surface, slowly rotate alternator rotor by hand. Observe ammeter reading. Field coil draw should be 4.75-6.0 amps (114 amp) or 4.5-6.5 amps (all others) at 14 volts.
- A low rotor coil draw indicates high resistance in field coil circuit (brushes, slip rings or rotor coil). A high rotor coil draw indicates possible shorted rotor coil or grounded rotor. No reading indicates an open rotor or defective brushes.