Circuit Operation - Charging Light Operation

One of the following requirements must be met in order to turn On the generator light.
1. When the voltage regulator is below 11.25 volts and rpm is greater than 1090 engine rpm.
2. When ignition is On and the generator is not turning. This is the bulb check.
3. There is also additional logic for certain diode failures, grounded or open stator, and open field windings or brushes.

A failure mode which leaves the generator with most of its output creates a situation in which the generator can regulate voltage most of the time. To the generator it looks like the vehicle has excessive loads. The result is a gradual loss of battery state of charge over a period of days during which the battery light would not come "On" because of the generators ability to regulate voltage.

Additionally, the Saturn charging system has a redundant ignition feed to the regulator in the event the bulb burns out. The generator will continue to charge, but the light will not illuminate during bulb check.