The White/GMC WHEB uses a 1157 bulb size for both front and rear turn signal applications. The replacement chart covers 1991 to 1995 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 the front and rear turn signals on the White/GMC WHEB across the 1991-1995 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 those markets.
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, 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 associated with the active turn signal function and the lower-wattage filament associated with a steady parking or position light function.
The 1157 uses a BAY15d bayonet base, which is an offset dual-contact bayonet mount. The offset pin arrangement prevents the bulb from being inserted in the wrong orientation, ensuring the correct filament is activated by each circuit.
Because the front and rear turn signal positions on the WHEB share the same bulb type, a single 1157 bulb serves as a direct replacement for all four turn signal positions on the vehicle.