Buick Regal Back Up Light Bulb Size

The Buick Regal back up light utilizes bulb sizes 921, 3157, 2458, 1156, P21W, and 890 depending on the specific version of the vehicle. Available data for the components spans from 1973 through 2017.

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
2014-2017	921
2011-2013	3157
1997-2004	1156
1988-1990	890
1973-1987	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921
ANSI standard (US & Canada). Dual-filament wedge bulb (T25). 12V, 27W/7W.	3157
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156
ANSI standard (US & Canada). Single-filament halogen bulb with PG13 base. 12V, 27W.	890

Other Locations

Additional Notes

The Buick Regal back up light specifications span four distinct bulb types across model years 1973 through 2017: the 921, 3157, 1156, and 890.
The 1156 is the most frequently specified bulb across the Regal lineup, covering model years 1973-1987 and 1997-2004. It is a single-filament bulb with a BA15s bayonet base, rated at 12V and 21W.
The BA15s bayonet base on the 1156 uses a single contact pin, which makes it physically incompatible with dual-contact bayonet sockets designed for other bulb types.
The 3157, specified for the Buick Regal for model years 2011-2013, is a dual-filament wedge bulb rated at 12V with a split wattage of 27W and 7W. In a back up light application, only the high-wattage filament is typically active.
The 921 wedge bulb, specified for the Regal for model years 2014-2017, uses a T15 wedge base and is rated at 12V and 16W. Wedge-base bulbs have no separate metal base and are held in place by the socket contacts gripping the glass envelope directly.
The 921 and 3157 both use wedge-style bases but are not interchangeable. The T15 and T25 designations indicate different body sizes, and their socket housings are sized accordingly.
The 890, specified for the Regal for model years 1988-1990, is a single-filament halogen bulb with a PG13 base, rated at 12V and 27W. The PG13 base is a prefocus-style fitting, distinct from both the bayonet and wedge bases used by the other bulb types in these specifications.
All four bulb types in these specifications conform to ANSI standards applicable in the United States and Canada, indicating standardized electrical and physical tolerances within those markets.
The shift from the 1156 bayonet base to the 890 halogen PG13 base between the 1987 and 1988 Regal model years represents a socket change, meaning the two bulbs are not drop-in substitutes for one another.
The transition from the 3157 dual-filament wedge to the 921 single-filament wedge between the 2013 and 2014 Regal model years also reflects a socket change, as the T25 and T15 wedge housings are sized differently and are not interchangeable.