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Alternator Output

CAUTION: DO NOT  start engine with "L" and "S" terminal connectors disconnected from alternator. DO NOT  allow "L" terminal to contact ground while engine is running.
  1. Turn ignition switch to OFF position. Connect positive voltmeter lead wire to alternator "B" terminal and negative wire to ground. See Figure. Ensure voltmeter indicates battery voltage. If voltmeter reads zero volt, an open circuit exists in wire between "B" terminal and battery positive terminal.
  2. Remove voltmeter. Disconnect negative battery cable. Remove output lead from alternator terminal "B". Install a 100-amp ammeter in series between "B" terminal and disconnected output lead. Install positive lead of ammeter to "B" terminal and negative lead to disconnected output wire.
  3. Install voltmeter in parallel between alternator "B" terminal and battery positive terminal. Install positive lead wire of voltmeter to "B" terminal and negative lead wire to positive terminal of battery. Reconnect negative battery cable.
  4. Install tachometer (if necessary) to monitor engine RPM. Start engine. Turn all lights and accessories on and depress brake pedal to load system. Increase engine speed to 2500-3000 RPM. Ensure alternator output is at least 35 amps.
  5. Observe voltmeter reading. If voltmeter indicates .2 volt and amperage output is at least 35 amps, system is okay. If voltage drop is greater than .2 volt, wiring is defective between alternator "B" terminal and battery positive terminal.
  6. Allow engine to idle. Turn off all accessories to remove load from system. Disconnect voltmeter. Connect negative lead of voltmeter to ground. Using positive lead of voltmeter, backprobe "S" terminal connector at rear of alternator.See Figure.
  7. Increase engine speed to 2500-3000 RPM. With no load on system, ammeter should read 5 amps or more. Battery voltage with no load at indicated speed should be 14.1-14.7 volts. If amperage output is less than indicated with or without load and no external faults exist in the alternator circuit, overhaul or replace alternator.
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