GMC 1999 Sierra 1500 Pickup Owner's Manual page 112

Features & Controls
beam lights with fog lamps at all times, or that headlights be turned on
whenever you must use your windshield wipers. In addition, most jurisdictions
prohibit driving solely with parking lights, especially at dawn or dusk. It is
recommended that you check with your own state or provincial highway
authority for applicable lighting regulations.
Headight High-Low Beam
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K2242
To change the headlights from low beam to high or high to low, pull the turn
signal lever all the way toward you. Then release it. When the high beams
are on, this blue light on the instrument panel also will be on.