Chrysler Full-Size Trucks 1997-2000 Repair Guide

General Information


The charging system incorporates the following major components:

Alternator drive belt
Electronic Voltage Regulator (EVR) circuitry in the PCM
Battery temperature sensor
Ignition switch
"Check Gauges" lamp
Voltmeter (if fitted)
Wiring harness and connections

The charging system is basically a series circuit with the battery wired in parallel. After the engine is started and running, the alternator takes over as the source of power and the battery then becomes part of the load on the charging system.

The alternator, which is driven by the belt, consists of a rotating coil of laminated wire called the rotor. Surrounding the rotor are more coils of laminated wire that remain stationary just inside the alternator case, the stator. When current is passed through the rotor via the slip rings and brushes, the rotor becomes a rotating magnet with, of course, a magnetic field. When a magnetic field passes through a conductor (the stator), alternating current (A/C) is generated. This A/C current is rectified, or turned into direct current (D/C), by the diodes located within the alternator.

The voltage regulator circuitry controls the alternator's field voltage by grounding one end of the field windings very rapidly. The frequency varies according to current demand. The more the field is grounded, the more voltage and current the alternator produces. Voltage regulation on these vehicles is located in the Powertrain Control Module (PCM).

Voltage is maintained at about 13.5-15 volts. During high engine speeds and low current demands, the regulator will adjust the voltage of the alternator field to lower the alternator output voltage. Conversely, when the vehicle is idling and the current demands may be high, the regulator will increase the field voltage, increasing the output of the alternator designed to reduce fuel consumption and increase power. A major factor in determining alternator output is the battery temperature sensor whose input to the PCM is used to adjust field voltage.

The charging system is turned on and off with the ignition switch. The system is on when the engine is running and the ASD relay is energized. When the ASD relay is on, the PCM supplies voltage to the alternator field coil.

The amount of current produced by the alternator is controlled by the EVR field control circuitry in the PCM. A battery temperature sensor, located in the battery tray housing, monitors battery condition. This information, along with data from monitored line voltage, is used by the PCM to vary charging rate.

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Fig. Back of typical alternator illustrating wiring

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Fig. Another style of alternator wiring