The GMC S15 uses the H6054 bulb size for both high beam and low beam headlights across all model years covered in the specifications, spanning 1982-1990.
The H6054 is a 5x7-inch rectangular sealed beam unit, meaning the lens, reflector, and filament are fused into a single glass housing rather than separated into distinct components.
Because the H6054 is a sealed beam design, the entire unit is replaced when the light fails, as opposed to halogen or HID systems where only an internal bulb is swapped out.
The H6054 operates at 12 volts, which is consistent with standard automotive electrical systems.
The H6054 carries ANSI standardization recognized in both the United States and Canada, meaning units from different manufacturers sharing this designation conform to the same physical and electrical specifications.
The shared H6054 fitment across both high beam and low beam positions on the GMC S15 indicates the vehicle uses a dual-function sealed beam arrangement rather than separate housings dedicated to each beam mode.