Oldsmobile Firenza Back Up Light Bulb Size

The Oldsmobile Firenza back up light uses bulb size 1156 or P21W depending on the specific version. Data for the bulb sizes covers the range from 1982 to 1988.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1982-1988	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The 1156 is the specified back up light bulb size for the Oldsmobile Firenza across all listed model years, spanning 1982-1988.
The 1156 is a single-filament bulb, meaning it serves one lighting function only, which is consistent with its application in a back up light circuit.
It operates at 12 volts and 21 watts, placing it in the mid-range of standard automotive incandescent output for reverse lighting purposes.
The 1156 uses a BA15s bayonet base, a single-contact mount where the "s" denotes a single pin, distinguishing it from the dual-contact BA15d variant.
The 1156 conforms to ANSI standards recognized in both the United States and Canada, indicating a standardized specification rather than a proprietary or regional-only part.
Because the BA15s base is a single-contact design, it is not interchangeable with physically similar bulbs that use a dual-contact bayonet base, such as the 1157, despite outward resemblance.