The Buick Gran Sport front turn signal requires either a 1157NA or 1034NA bulb size, while the rear turn signal uses a 1157 bulb size. The replacement chart covers 1965 through 1967 production 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 Buick Gran Sport turn signal specifications cover the 1965-1967 model years, spanning both front and rear positions.
All three bulb types listed across these specifications, the 1157NA, 1034NA, and 1157, share the BAY15d bayonet base and a dual-filament design operating at 12V with a 21W/5W output rating.
The dual-filament construction of these bulbs allows a single unit to serve two functions, typically running light duty on the lower-wattage 5W filament and turn signal or braking duty on the higher-wattage 21W filament.
The BAY15d base is an offset double-contact bayonet fitting, where the two contact pins are positioned at different heights to prevent incorrect installation orientation.
The 1157NA and 1034NA carry the "NA" suffix, which denotes natural amber glass rather than a clear envelope, meaning the amber color is built into the glass itself rather than produced by a colored lens or coating.
The 1034NA is specified as a variant of the 1157, sharing the same base type and voltage and wattage ratings, though it carries a distinct ANSI designation.
For the Buick Gran Sport, the front turn signal position used the 1157NA in 1966-1967 but the 1034NA in 1965, indicating a fitment difference between the 1965 model year and the two years that followed.
The rear turn signal position used the 1157 across all three years, 1965-1967, without variation.
The 1157 used at the rear position differs from the front-position 1157NA in that it lacks the natural amber glass, making the two bulbs not directly interchangeable where amber coloration is required by the front housing design.
All bulb types listed conform to ANSI standards applicable in both the United States and Canada.