Alternator Lamp/Indicator: Description and Operation

When the ignition switch is in Start or Run position, battery current flows through the alternator warning indicator into regulator at terminal 1 and to ground through the indicator switch. The electronic control measures a low voltage at terminal A and closes the field switch. This applies battery voltage to the field through alternator terminal F. With current in the field and the rotor turning, alternator stator produces a voltage at terminals B and S.
A predetermined voltage at terminal S operates the electronic control to open indicator switch, which removes ground from alternator warning indicator.
Alternator current output is controlled by current in the field. Average field current depends on length of time field switch is closed. The electronic control closes field switch when voltage at terminal A is low and opens switch when voltage is high.