The White/GMC WIL uses a 1157 bulb size for both front and rear turn signal applications. The replacement chart covers 1988 through 1992 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 is the sole bulb type specified for both front and rear turn signals on the White/GMC WIL across the 1988-1992 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 those markets.
As a dual-filament bulb, the 1157 contains two separate 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, which is consistent with standard automotive DC voltage found in most commercial and light-duty vehicles.
The two filaments in the 1157 are rated at 21 watts and 5 watts respectively, with the higher-wattage filament typically handling the turn signal or brake function and the lower-wattage filament handling the parking or running light function.
The 1157 uses a BAY15d bayonet base, which is a double-contact bayonet mount with offset pins. The offset pin design prevents the bulb from being inserted in the wrong orientation, ensuring each filament connects to its correct circuit.
Because the BAY15d base uses offset pins, it is not interchangeable with single-contact bayonet bases or with double-contact bases that use symmetrically placed pins, such as the BAY15s or the BA15d.
The 1157 is sometimes cross-referenced with the 2057 bulb, though the 2057 has a lower-wattage low filament (rated at approximately 26.9W/8W in some standards), making direct substitution a matter of circuit compatibility rather than physical fit alone.