1998 GMC Sonoma Owner's Manual - Page 121

Voltmeter Gage When your engine is not running, but the ignition is on (in RUN), this gage shows your battery's state of charge in DC volts. You can only drive for a short time with the reading in either warning zone. If you must drive, turn off all unnecessary accessories. Readings in either warning zone indicate a possible problem in the electrical system. Have the vehicle serviced as soon as possible. Shift Light You have the shift light if you have a manual transmission. This light comes on very briefly as a bulb check when you start the engine. Shifting when the indicator light is on will help you get the best fuel economy. See "ShiftLight" in the Index. 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 in large number of electrical accessories are operating 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 providefull 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. 2-57