White/GMC WCM front side marker bulbs use 1157 size while rear side marker bulbs use 194 size. Replacement chart data covers 1988 to 1994 production years with 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 WCM uses two distinct bulb types across its side marker positions: the 1157 for front side markers and the 194 for rear side markers, covering model years 1988-1994 for both positions.
The 1157 is a dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base.
The BAY15d bayonet base on the 1157 features offset pins, which physically prevents installation of single-filament bayonet bulbs that share a similar base profile but carry different pin positions.
The dual-filament design of the 1157 allows it to serve two lighting functions within a single housing, which is why it is a common choice for front marker positions that may also carry a turn or running light function.
The 194 is a miniature wedge bulb of the T10 form factor, rated at 12V and 3.78W, and it uses a wedge-style base rather than a bayonet mount.
The T10 wedge base of the 194 is held in its socket by the tension of the base itself rather than by a locking mechanism, making it a tool-free bulb in most housing designs.
Both the 1157 and the 194 conform to ANSI standards applicable in the United States and Canada, meaning their electrical and physical specifications follow a regulated baseline.
The 1157 and the 194 are not interchangeable with each other, as they differ in base type, wattage, filament count, and physical form factor.
The significant wattage difference between the 1157 (21W/5W) and the 194 (3.78W) reflects their respective roles, with the higher-output 1157 suited to front marker positions and the lower-output 194 used at the rear.