The White/GMC WCM uses 1157 bulb size for both front and rear turn signal applications. Replacement chart data covers 1988 to 1994 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 WCM uses the 1157 bulb for both its front and rear turn signals across the 1988-1994 model years.
The 1157 is an ANSI-standardized bulb type recognized across the United States and Canada, meaning it conforms to a defined set of electrical and physical characteristics shared by all compliant manufacturers.
The 1157 is a dual-filament bulb, which means it contains two separate filaments within a single envelope, allowing it to serve two distinct lighting functions from one unit.
The bulb operates on a 12-volt electrical system and carries a wattage rating of 21W on its high-intensity filament and 5W on its low-intensity filament, corresponding to its turn signal and parking light roles respectively.
The 1157 uses a BAY15d bayonet base, a two-pin offset base design that physically prevents incorrect insertion, as the two pins are positioned at different heights to ensure proper filament alignment.
Because the front and rear turn signal positions on the WCM share the same 1157 specification across all listed model years, a single bulb type serves all four turn signal sockets on the vehicle.
The BAY15d base of the 1157 is not interchangeable with single-filament bayonet bases such as the BA15s, which lacks the offset dual-pin configuration required for dual-filament operation.