The White/GMC WXLM uses 1157 bulb size for both front and rear turn signal applications. The replacement chart covers 1991 to 1993 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 1157 bulb is the sole bulb type listed across all turn signal positions for the White/GMC WXLM, covering both front and rear applications for the 1991-1993 model years.
The 1157 is a dual-filament bulb, meaning it carries two separate filaments within a single envelope, allowing it to serve two distinct lighting functions at different wattages.
The bulb operates on a 12-volt electrical system and draws 21 watts on its primary filament and 5 watts on its secondary filament, reflecting the higher power demand of the turn signal function versus a lower-intensity mode.
The 1157 uses a BAY15d bayonet base, which is an offset twin-pin base design. The offset pin placement is a deliberate fitment control, preventing incorrect single-filament bulbs with similar bases from being seated in the socket.
The 1157 conforms to ANSI standards and is recognized in both the United States and Canada, placing it within a widely standardized specification used across North American vehicle production.
Because the 1157 is shared across both the front and rear turn signal positions for all three listed model years, a single bulb type services all four turn signal sockets on the vehicle.
The BAY15d base of the 1157 is not interchangeable with the BAY15s base found on single-filament bulbs such as the 1156, despite a superficial physical resemblance. Substituting a single-filament bulb in a dual-filament socket would result in incomplete circuit function.