The GMC Sprint front and rear turn signal bulbs both require a 1157 size bulb for proper operation. The replacement chart covers vehicle production spanning 1971 to 1977.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC Sprint uses the 1157 bulb for both its front and rear turn signals across the 1971-1977 model years.
The 1157 is an ANSI-standardized bulb type recognized across the United States and Canada.
It is a dual-filament bulb, meaning it contains two separate filaments within a single glass envelope, allowing it to serve two distinct lighting functions at different wattages.
The 1157 operates on a 12-volt electrical system, consistent with standard automotive electrical architecture of that era.
Its two filaments draw 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 running or parking light function.
The 1157 uses a BAY15d bayonet base, which features two offset pins at different heights on the base to ensure correct rotational orientation during installation, preventing the filaments from being connected to the wrong circuits.
Because the front and rear turn signal positions on the GMC Sprint share the same bulb type, a single 1157 bulb serves as a direct fitment for all four turn signal sockets on the vehicle.
The BAY15d base is not interchangeable with single-filament bayonet bases such as the BA15s, as the dual-pin offset configuration is specific to dual-filament applications.