The White/GMC WIS uses a 1157 bulb size for front side marker applications and a 194 bulb size for rear side marker positions. Replacement chart data spans 1988 to 1991 model 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 WIS uses two distinct bulb types across its 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 with a BAY15d bayonet base, rated at 12V with a 21W/5W output, meaning it operates one filament for running light functions and a brighter filament for signaling.
The BAY15d base on the 1157 features offset pins, which physically prevents installation of single-filament bayonet bulbs that share a similar base profile but lack the second filament contact.
The 1157 conforms to ANSI standards recognized in both the United States and Canada, indicating a standardized specification for electrical and photometric performance.
The 194 is a miniature wedge-type bulb in the T10 form factor, rated at 12V and 3.78W, designed for low-current marker and clearance light applications.
The T10 wedge base of the 194 relies on its lead wires bent against the socket walls for retention, rather than a locking bayonet mechanism, making it incompatible with bayonet-style sockets used by the 1157.
The 194 also conforms to ANSI standards for the United States and Canada, placing it within the same regulatory framework as the 1157 despite the significant difference in wattage and base type.
Because the front marker position on the White/GMC WIS uses the dual-filament 1157, substituting a single-filament bulb of a similar base type would result in the loss of one lighting function at that position.
The 194 at the rear side marker position draws considerably less power than the 1157, reflecting the lower luminance requirement typical of rear side marker applications compared to front combined marker and turn signal positions.