Alternator Output Test

NOTE: A slightly discharged battery should be used as a fully charged battery may not allow full alternator output.

Turn ignition off. Disconnect negative battery cable. Disconnect alternator output wire from terminal "B". Connect positive lead of 100-amp ammeter to terminal "B" and negative lead to disconnected output lead.
CAUTION: Tighten each connection securely as heavy current flow will exist. DO NOT use clips on ammeter. An inductive-type ammeter is recommended.
Connect positive voltmeter lead (0-20 volts) to alternator terminal "B" and negative lead to ground. Install tachometer, and reconnect negative battery cable.
Ensure voltmeter indicates battery voltage. If voltage is not present, check for open circuit in wire between alternator terminal "B" and negative battery terminal. Check grounds and fusible link.
Start engine and turn headlights on. Set headlights at high beam and heater blower switch on HIGH. Increase engine speed to 2500 RPM and note alternator output current on ammeter. Minimum output should be within specification. See ALTERNATOR MINIMUM OUTPUT SPECIFICATIONS table.
NOTE: Output voltage changes with electrical load and temperature. Ensure proper electrical load is applied while checking output. Nominal output may not be obtained if alternator or ambient temperature is excessive. Allow alternator or temperature to cool, and recheck output. Alternator output is stamped on metal plate attached to alternator case.
If minimum output is not obtained and alternator wiring is okay, repair alternator. Operate engine at idle speed after the test.

ALTERNATOR MINIMUM OUTPUT SPECIFICATIONS