The White WCM front side marker bulb size measures 1157 or 194, while the rear side marker bulb size measures 194 for this truck model. The replacement chart covers 1981 through 1988 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 WCM uses two distinct bulb types across its front and rear side marker positions: the 194 and the 1157, both of which conform to ANSI standards recognized in the United States and Canada.
The 194 bulb is a miniature wedge type with a T10 form factor, rated at 12V and 3.78W, making it a low-wattage single-filament lamp suited to marker and clearance lighting applications.
The 1157 bulb operates on a dual-filament design with a BAY15d bayonet base, rated at 12V with filaments drawing 21W and 5W respectively, which allows it to serve both a brighter active state and a dimmer standing light function.
The rear side marker position on the White WCM uses the 194 bulb across all model years from 1981-1988 without variation.
The front side marker position also uses the 194 bulb for model years 1981-1987, establishing it as the predominant front marker bulb across that span.
The 1988 White WCM front side marker departs from the 194 specification, requiring the 1157 bulb instead, which carries a physically different BAY15d bayonet base rather than a wedge-style fitting.
Because the 194 uses a wedge base and the 1157 uses a BAY15d bayonet base, the two bulbs are not interchangeable, and substituting one for the other in the 1988 front side marker position would require a socket incompatible with the alternate type.
The dual-filament nature of the 1157 means the 1988 front side marker socket on the White WCM is wired to support two separate circuits, a configuration absent from the 194-based sockets used in all other positions.