Cadillac Fleetwood Back Up Light Bulb Size

The Cadillac Fleetwood back up light utilizes bulb sizes 2057, 3057, P21W, and 1156 depending on the specific production period for the vehicle. Available information covers the range from 1965 through 1996.

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
1993-1996	2057
1989-1992	3057
1965-1988	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. Brighter variant of 1157. 12V, 26.9W/8W.	2057
ANSI standard (US & Canada). Dual-filament wedge bulb (T25). 12V, 27W/7W.	3057
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The Cadillac Fleetwood back up light specifications cover three distinct bulb types across the model's history: the 1156, 3057, and 2057.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base. It is the most widely specified bulb in the Cadillac Fleetwood back up light application, covering the 1965-1988 model years.
The 3057 is a dual-filament bulb in a T25 wedge form, rated at 12V with filaments drawing 27W and 7W respectively. It was specified for the Cadillac Fleetwood from 1989-1992.
The 2057 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with filaments drawing 26.9W and 8W. It was specified for the 1993-1996 model years.
All three bulb types conform to ANSI standards recognized in both the United States and Canada.
The 1156 uses a BA15s single-contact bayonet base, while the 2057 uses a BAY15d dual-contact bayonet base. These two base types are not interchangeable despite their physical similarity, as the BAY15d features offset pins to prevent incorrect installation.
The 3057 uses a wedge-style base, which is mechanically distinct from the bayonet bases found on both the 1156 and 2057, making cross-substitution between these groups physically incompatible.
The 2057 is described as a brighter variant of the 1157 bulb. Its higher-wattage filament draws 26.9W compared to the 1156's single 21W filament, meaning the 2057 produces more light output in its primary filament mode.
The transition from the single-filament 1156 to the dual-filament 3057 in 1989 represents a change in the electrical configuration of the back up light circuit, as dual-filament bulbs serve two independent lighting functions within a single housing.
The subsequent shift from the 3057 to the 2057 in 1993 retained the dual-filament configuration but changed the base type from a wedge to a BAY15d bayonet, indicating a socket change in the Fleetwood's tail lamp assembly at that point.