GMC Sierra Owners Manual
Headlamp High/ Low-Beam Changer
(Headlamp High/Low Beam Changer): To change the headlamps from low to high beam, push the lever toward the instrument panel. To return to low-beam headlamps, pull the multifunction lever toward you. Then release it.
When the high beams are on, this indicator light on the instrument panel cluster will also be on.