The Bertone X-1/9 front turn signal bulb measures 1157 in size while the rear turn signal bulb measures P21W in size. The replacement chart covers 1984 to 1989 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 Bertone X-1/9 uses two distinct bulb types across its front and rear turn signal positions for the 1984-1989 model years, with each position requiring a specific and non-interchangeable bulb.
The 1157 is an ANSI-standard bulb used in North American markets, operating at 12V with a dual-filament configuration rated at 21W and 5W respectively, mounted on a BAY15d bayonet base.
The dual-filament design of the 1157 allows it to serve two lighting functions from a single housing, with the higher-wattage filament typically handling the turn signal function and the lower-wattage filament handling a secondary function such as parking or running light.
The P21W follows the ECE standard used in European and international markets, operating at 12V with a single filament rated at 21W, mounted on a BA15s bayonet base.
The front turn signal position on the Bertone X-1/9 calls for the 1157 bulb across all six model years covered in the specifications, from 1984 through 1989.
The rear turn signal position on the Bertone X-1/9 calls for the P21W bulb across all six model years covered in the specifications, from 1984 through 1989.
The 1157 and P21W are not interchangeable despite sharing a similar 21W output rating, as they use different bayonet base types: BAY15d for the 1157 and BA15s for the P21W.
The BAY15d base used by the 1157 features offset pins to ensure correct polarity orientation, a physical characteristic that distinguishes it from the symmetrical BA15s base of the P21W.