the gauge lights are activated and dimmed [to off] by turning the light switch knob [also the interior light], the rheostatic mechanism at the front of the switch may be dirty/corroded/broke, or you may have broken wires or a bunch of missing/burned out bulbs - the light bulbs are in holes in the back of the cluster, you won't see them unless you crawl under there or take the gauges out ... the GMC logo in the dash is provision for an option, like tach or vacuum gauge in bigger trucks .... and GMCs are different than Chevys, always specify
Bill
