The White/GMC WIL uses a 1157 bulb size for front side marker applications and a 194 bulb size for rear side marker positions. The replacement chart covers 1988 through 1992 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The White/GMC WIL uses two distinct bulb types across its side marker positions: the 1157 for front side markers and the 194 for rear side markers, covering the 1988-1992 model years for both positions.
The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 21W/5W output, meaning it operates one filament at higher wattage and a second at lower wattage depending on the circuit demand.
The BAY15d bayonet base of the 1157 features offset pins, a design that prevents incorrect insertion and ensures polarity-sensitive dual-filament bulbs are seated in the correct orientation.
The 194 is a miniature wedge-style bulb in the T10 form factor, rated at 12V and 3.78W, making it a low-output single-filament unit suited to low-intensity marker applications.
Both the 1157 and 194 are ANSI-standardized bulbs recognized in both the United States and Canada, meaning their electrical and physical specifications conform to a defined industry standard rather than a proprietary format.
The 1157 and 194 use fundamentally different base types, a bayonet mount versus a wedge mount, making them physically non-interchangeable despite both operating on a 12V system.
The wattage difference between the two bulbs is substantial: the 1157 draws up to 21W on its primary filament, while the 194 draws only 3.78W, reflecting their different roles in front versus rear marker lighting.
Because the 1157 is a dual-filament bulb, a single-filament replacement of the same base type would not replicate full functionality if both filaments are utilized by the vehicle's circuit.