The White/GMC WHS features front side marker bulbs in 1157 size and rear side marker bulbs in 194 size. The replacement chart covers 1988 to 1991 production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The White/GMC WHS uses two distinct bulb types across its front and rear side marker positions for the 1988-1991 model years: the 1157 at the front and the 194 at the rear.
The 1157 is a dual-filament bulb, meaning it contains two separate filaments within a single envelope, each rated at a different wattage. Its ratings are 21W for the primary filament and 5W for the secondary filament, operating at 12V.
The 1157 uses a BAY15d bayonet base, a two-pin offset base design. The offset pin placement is a deliberate fitment feature that prevents incorrect insertion of the bulb into the socket.
Because the 1157 is a dual-filament type and the front side marker position on the White/GMC WHS uses it across all four listed model years, the socket at that position is wired to accommodate both filaments.
The 194 is a miniature wedge-type bulb in the T10 form factor. Unlike the 1157, it has no base pins and is instead held in place by the tension of the socket walls gripping the wedge-shaped glass envelope.
The 194 is a single-filament bulb rated at 3.78W and 12V, making it significantly lower in wattage than the 1157 used at the front.
Both the 1157 and the 194 conform to ANSI standards applicable in the United States and Canada, indicating standardized electrical and physical specifications across manufacturers.
The 1157 and the 194 are not interchangeable with each other. They differ in base type, filament count, wattage, and physical form factor, and each is specific to its respective marker position on the WHS.
The rear side marker position on the White/GMC WHS calls for the 194 across the 1988-1991 model years, indicating a consistent socket specification at that location throughout the listed production span.
The T10 designation of the 194 refers to a tubular bulb form with a width of approximately 10 millimeters, a standard sizing classification used in the ANSI bulb nomenclature system.