The Buick Somerset brake light requires a unique 2057 bulb size for the lighting system. Data for the specific bulb requirements covers the range from 1986 to 1987.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Buick Somerset uses the 2057 bulb for the brake light position across both the 1986 and 1987 model years.
The 2057 is an ANSI-standard dual-filament bulb rated at 12V with a high/low filament draw of 26.9W and 8W respectively, mounted on a BAY15d bayonet base.
The 2057 is a brighter variant of the 1157, sharing the same BAY15d bayonet base, which means the two types are physically interchangeable in terms of socket fitment, though their wattage outputs differ.
The 1157 carries a lower filament rating of 21W and 5W compared to the 2057, making the two bulbs functionally distinct despite their shared base type.
The Center High Mount Stop Light on the 1987 Buick Somerset uses the 1157 bulb, while the same position on the 1986 model uses the P21W bulb.
The P21W follows the ECE standard used in European and worldwide markets, whereas the 1157 follows the ANSI standard used in the United States and Canada, meaning the two bulbs originate from different regulatory frameworks.
The P21W is a single-filament bulb with a BA15s bayonet base, rated at 12V and 21W, which is a different base type from the BAY15d base found on both the 1157 and 2057.
Because the P21W uses a BA15s base and the 1157 uses a BAY15d base, the two bulbs specified for the Center High Mount Stop Light across the 1986 and 1987 model years are not directly interchangeable without a socket adapter.