1998 GMC Safari Owner's Manual - Page 160

Rear Window Defogger (Option) If your vehicle has this option, the rear window will have lines running across the glass. These lines heat your window. For best results, clear the window as much snow or of ice as possible before using the rear window defogger. To turn on the rear window defogger, find the button to the leftof the heater controls with the defog symbol onit. will The rear window defogger only work when the ignition switchi6 in the RUN position. You can turn the defogger off any time by pressing at the button again. The defogger will shut itself after off several minutes so that the glass does not get too hot. If the window still isn't clear, turn the defogger on again. Do not attach a temporary vehicle license, tape decals or across the defogger grid the rear window. on 1 NOTICE: Don't use a razor blade something else sharp or If you on the inside of the rear window. do, you could cut or damage the defogger and the repairs would not be covered by your warranty. Press the button until the light comes on, then release it.