The White/GMC WCA front and rear turn signal bulbs both utilize a 1157 size bulb configuration. The replacement chart covers vehicle production spanning 1988 to 1995.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 1157 is the sole bulb type specified for the White/GMC WCA across both front and rear turn signal positions for the 1988-1995 model years.
The 1157 is an ANSI-standardized bulb recognized in both the United States and Canada, meaning it conforms to a defined set of electrical and physical standards shared across North American markets.
The 1157 is a dual-filament bulb, which means it contains two separate tungsten filaments within a single envelope, allowing it to serve two distinct lighting functions from one unit.
The 1157 operates on a 12-volt electrical system, consistent with the standard automotive DC voltage found in most conventional passenger and commercial vehicles.
The two filaments in the 1157 are rated at 21 watts and 5 watts respectively, with the higher-wattage filament typically assigned to the active turn signal function and the lower-wattage filament to a secondary role such as a parking or position light.
The 1157 uses a BAY15d bayonet base, a two-pin offset base design in which the two pins are positioned at different heights along the base to prevent incorrect installation orientation.
Because the BAY15d base is offset, it is not interchangeable with the BAY15s single-filament bayonet base, even though the physical housing may appear similar in size.
The consistent use of the 1157 across all listed model years for both front and rear positions means a single bulb specification applies to the full 1988-1995 production range of the WCA.