GM Service Manual Online
For 1990-2009 cars only

The charging system consists of the following components:

    • The battery
    • The generator
    • The voltage regulator
    • The indicator lamp or the voltmeter circuitry

The generator supplies the electrical power for charging the battery and for operating the accessories.

AD-Series Generators


Object Number: 396186  Size: SH

AD-230 and AD-244 Series generators feature a high ampere output per pound of weight. The A stands for air cooling. The D stands for dual internal fans. The 2 stands for Gen II while the 30 and 44 are the measurements, in millimeters, of the outside diameter of the stator laminations. Neither generators are serviceable and must be replaced


Object Number: 396187  Size: SH

The charge indicator turns on when the ignition switch is closed and the engine is not running, and turns off when the engine is running. If the charge indicator is on with the engine running, this indicates a charging system condition. The indicator will glow at full brilliance, not half lit, if any of the following conditions occur:

    • Any charging condition
    • System voltage is too high or too low

Object Number: 74064  Size: SH

The regulator limits system voltage by controlling the rotor field current. When the field current is on, the regulator switches the rotor field on and off at a fixed rate of about 400 cycles per second. By varying the overall on/off time, correct average field current for proper system voltage control is maintained. At high speeds, the on time may be 10 percent and the off time may be 90 percent. At low speeds, and with high electrical loads, the on/off time may be 90 percent and 10 percent respectively.

The regulator has four terminals-- P, L, I, and S. On all P applications, P, L, I/F, and S is stamped on the regulator.

The L terminal turns on the regulator and allows field current flow when the switch is closed. The L terminal must connect through an indicator lamp or a suitable resistor.

The F terminal is used to monitor the duty cycle and is used with an engine speed boost at idle.

The P terminal connects internally to the stator and may be wired to a tachometer or other device. The S terminal may be used to "sense" voltage at another location on the vehicle for voltage control. If the S terminal is not used, the generator will use an integrated circuit in the regulator to "sense" voltage.

P model vehicles use a voltmeter in place of an indicator lamp. For schematics of the specific generator circuits, refer to Starting and Charging Schematics.