Undercharged Battery

With ignition switch "ON", connect a voltmeter from alternator "BAT" terminal to ground, then from No. 1 terminal to ground, and last, No. 2 terminal to ground. A zero reading indicates an open between connection and battery.
Opens in the No. 2 lead may be between terminals at the crimp between harness wire and terminal, or in wire. See Fig 1.
NOTE: If preceding test is satisfactory, continue to next step.
Disconnect battery ground cable. Connect an ammeter in circuit at "BAT" terminal of alternator.
Reconnect battery ground cable. Turn on all available accessories. Connect a carbon pile across battery. Operate engine at moderate speed and adjust carbon pile as required to obtain maximum current output.
If ampere output is within 10 amps of rated output as that stamped on the alternator case, the alternator is good. Refer to the ALTERNATOR OUTPUT SPECIFICATIONS table.
If output is not within 10 amps of rated output, ground field winding by inserting a screwdriver into test hole. See Fig 1.

Fig 1: Delcotron Terminal Locations & I.D. (All Models) Visually inspect all terminals for clean and tight connections.

CAUTION: Tab is within 3/4" (19 mm) of casting surface. DO NOT force screwdriver deeper than 1" (25 mm) into end frame. If test hole is not accessible, proceed to "Testing (On Bench)" as described under Overhaul.
Operate engine at moderate speed as required and adjust carbon pile for maximum output.
If output is now within 10 amps of rated output with fields grounded, regulator is defective and requires replacement.
If output is still not within 10 amps of rated output, check field winding, diode trio, rectifier bridge, and stator.