Undercharged Battery

With ignition switch in "ON" position, connect a voltmeter from alternator "BAT" terminal to ground. See Fig 1. Next, connect a voltmeter from No. 1 terminal to ground and then from No. 2 terminal to ground. A zero reading indicates an open between voltmeter connection and battery.

Fig 1: Identification of Delcotron Terminal Locations 10 SI alternator is shown.

NOTE: Alternators have a built-in feature, that avoids overcharging or accessory damage by preventing alternator from turning on if there is an open in wiring harness connected to No. 2 alternator terminal.
Opens in wiring harness connected between No. 2 terminal and battery may be between terminals, at crimp between harness wire and terminal, or in wire. If test results are satisfactory, proceed to step 3.
Disconnect battery ground cable. Connect an ammeter in series between "BAT" terminal of alternator and disconnected "BAT" lead. See Fig 2. Reconnect battery ground cable and turn all accessories on.

Fig 2: Alternator Connections for Bench Testing & On-Vehicle Check of Undercharged Battery
Connect a carbon pile across battery. Operate engine at a speed of 2000 RPM and adjust carbon pile as necessary to obtain maximum current output.
If ampere output is within 10 amps of rated output stamped on alternator case, alternator is good. If output is not within 10 amps of rated output, ground field winding tab by inserting a screwdriver into end frame test hole. See Fig 3.

Fig 3: View of Field Ground Tab Accessible Through Hole in End Frame

CAUTION: Tab is within 3/4" of casting surface. DO NOT force screwdriver deeper than 1" into end frame.
Operate engine at a speed of 2000 RPM and adjust carbon pile as required to obtain maximum current output. If output is now within 10 amps, check field windings, diode trio, and voltage regulator. If output is not within 10 amps of rated output, check field windings, diode trio, rectifier bridge, and stator.

NOTE: If test hole is not accessible, disassemble alternator and test components.