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No-Load Test

  1. Disconnect battery-to-alternator terminal "B" wire. See Fig 1. Using an ammeter and voltmeter, connect negative ammeter lead to disconnected alternator terminal "B" wire end, and connect positive ammeter lead to alternator terminal "B".
  2. Connect voltmeter positive lead to alternator terminal "B" and negative lead to ground. See Fig 1. Start engine and increase engine speed to 2000 RPM. Both meters should read within specification. See ALTERNATOR REGULATED OUTPUT SPECIFICATIONS  table.
  3. If voltage is more than specified, replace IC regulator. If voltage is less than specified, ground "F" (full field) terminal. See Fig 2. If voltage is more than specified range, replace IC regulator. If voltage is less than specified range, repair or replace alternator.
ALTERNATOR REGULATED OUTPUT SPECIFICATIONS (AT 2000 RPM)

Temperature Amps Volts
77°F (25°C) 10 Or Less 13.9-15.1
239°F (115°C) 10 Or Less 13.5-14.3
Fig 1: Testing Charging Circuit
G93F02148Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Fig 2: Testing Alternator Full Field Output
G93H82153Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002