Saturn SC Back Up Light Bulb Size

Additional Notes

• The Saturn SC uses two different back up light bulb types across its 1991 and 1992 model years, with each year requiring a distinct and non-interchangeable bulb.
• The 1992 Saturn SC takes a P21W bulb, an ECE-standard single-filament signalling bulb rated at 12V and 21W with a BA15s bayonet base.
• The BA15s base found on the P21W features a single contact pin, which physically prevents it from being substituted with dual-pin bayonet bulbs without modification.
• The 1991 Saturn SC takes a 2057 bulb, an ANSI-standard dual-filament bulb rated at 12V with a high/low output of 26.9W and 8W respectively, fitted with a BAY15d bayonet base.
• The BAY15d base on the 2057 uses two offset contact pins, a design that ensures polarity-correct installation and distinguishes it from the single-pin BA15s base used in the 1992 application.
• Because the P21W and 2057 use different base types, BA15s and BAY15d respectively, the two bulbs are not interchangeable between model years.
• The 2057 is a brighter variant of the 1157 bulb, sharing the same BAY15d base but drawing more wattage on its high-intensity filament at 26.9W versus the 1157's 26.9W rating, with the 2057 distinguished by its higher candela output.
• The P21W follows ECE regulations, a standard widely adopted outside North America, while the 2057 follows ANSI standards, the governing specification for automotive lighting in the United States and Canada.