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Undercharged Or Overcharged Battery

CAUTION: To prevent injury and/or damage to vehicle, disconnect negative battery cable before connecting or disconnecting a series type ammeter to alternator.
NOTE: Ensure battery is fully charged and in good condition before performing the following steps. If battery is not at (or near) a fully charged condition, or if its condition is questionable, substitute a known good battery before proceeding.
  1. Turn ignition and all accessories off. Measure battery voltage and record for use in step 2). Disconnect alternator connector. Turn ignition on. Using a DVOM, connect positive voltmeter lead to alternator terminal "L" and negative lead to ground. On vehicles with gauges, also connect DVOM to alternator terminals "F" or "I". See WIRING DIAGRAMS  . If battery voltage is present at terminal(s), turn ignition off, connect alternator harness connector and go to next step. If battery voltage is not present, check and repair open in circuit between alternator terminal(s) and battery.
    CAUTION: Carbon pile testing is part of this procedure. To avoid battery explosion, turn carbon pile OFF before connecting to or disconnecting from vehicle battery.
  2. Disconnect negative battery cable. Connect ammeter to alternator output (BAT) terminal. Connect negative battery cable. With load off, connect carbon pile load tester across battery terminals. Start engine and slowly increase to approximately 1500 RPM. Measure voltage between battery terminals. If voltage is between 16 volts and battery voltage measured in step 1), go to step 4). If voltage is not between 16 volts and battery voltage, go to next step.
  3. If voltage is greater than 16 volts, check alternator terminal "S" circuit, if used, for high resistance or a bad connection. Repair circuit and/or bad connection as needed. If circuit is okay or not used and voltage is greater than 16 volts or less than battery voltage measured in step 1), replace alternator.
  4. With engine at approximately 1500 RPM, turn accessories on and load battery with carbon pile load until maximum alternator output is reached. Adjust the carbon pile to maintain 13 volts or more. Measure the amperage output. If amperage output is within 15 amps of rated output, alternator is okay. If amperage output is not within 15 amps of rated output, repair or replace the alternator. Refer to the ALTERNATOR USAGE/AMP OUTPUT RATING  table.
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