The Buick GS front turn signal uses a 1157NA bulb size while the rear turn signal requires a 1157 bulb size. The replacement chart covers 1970 to 1972 model years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 1157 and 1157NA bulbs are the two types specified for the Buick GS across the 1970-1972 model years, with the 1157NA assigned to front turn signals and the standard 1157 assigned to rear turn signals.
Both bulb types follow the ANSI standard recognized in the United States and Canada, and both operate on a 12-volt electrical system with a dual-filament configuration rated at 21 watts and 5 watts respectively.
The higher 21-watt filament in each bulb serves the active turn signal function, while the lower 5-watt filament serves a secondary purpose such as a parking or running light.
Both types share the BAY15d bayonet base, a two-pin offset base design that physically locks the bulb into the socket and ensures correct filament orientation.
The distinguishing feature of the 1157NA is its natural amber glass envelope, which produces an amber light output directly from the bulb itself rather than relying on a colored lens.
Because the 1157NA and 1157 share the same BAY15d base and identical wattage ratings, the two types are physically interchangeable in terms of socket fitment, though substituting a clear 1157 in place of an 1157NA would alter the color output at the front turn signal position if the lens is also clear.