Voltmeter Inaccurate
WARNING: This page does not describe the selected car, but rather 11 other vehicles, including the 1999 GMC Yukon, 1999 GMC Suburban, 1999 GMC Pickup, 1999 GMC Cab & Chassis, and 1999 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.
Turn ignition on. Connect voltmeter between positive and negative battery terminals. If voltage reading is about the same as vehicle's voltmeter, vehicle voltmeter is okay. If voltage reading is different from vehicle's voltmeter, replace instrument cluster.