1999 GMC Safari Owner's Manual - Page 131

yellowblue Charging System Indicator Light The charging system light will come on briefly when you turn the ignition on, but the engine is not running, as a check to show you the light is working. Then it should go out once the engine is running. If it stays on, or comes on while you are driving, you may have a problem with the electrical charging system. It could indicate that you have a loose accessory drive belt, or another electrical problem. Have it checked right away. Driving while this light is on could drain your battery. If you must drive a short distance with the light on, be certain to turn off all your accessories, such as the radio and heater/air conditioner. Voltmeter When your engine is not running, but the ignition is on (in the RUN position), the gage shows your battery's state of charge in DC volts. When the engine is running, the gage shows the condition of the charging system. Readings between the low and high warning zones indicate the normal operating range. Readings in the low warning zone may occur when a large number of electrical accessories are operating in the vehicle and the engine is left at an idle for an extended period. This condition is normal since the charging system is not able to provide full power at engine idle. As engine speeds are increased, this condition should correct itself as higher engine speeds allow the charging system to create maximum power. 2-61