Buick GS 455 Back Up Light Bulb Size

The Buick GS 455 back up light requires bulb size 1156 or P21W depending on the specific application. Data for the bulb size chart covers the range from 1970 to 1972.

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
1970-1972	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 sole bulb type listed for the Buick GS 455 backup light across the 1970-1972 model years.
The 1156 is an ANSI-standardized bulb recognized in both the United States and Canada, meaning it conforms to a defined set of electrical and physical specifications shared across those markets.
It operates on a 12-volt system and draws 21 watts, which is typical of single-filament incandescent bulbs used in dedicated backup light applications.
The 1156 uses a BA15s bayonet base, a single-contact mount where the bulb is inserted and twisted to lock into place, as opposed to a screw or wedge base design.
Because the 1156 is single-filament, it serves only one lighting function per socket, distinguishing it from dual-filament variants such as the 1157, which handles two functions from a single housing.
The BA15s base designation indicates a 15mm bayonet cap with a single contact pin, and substituting a bulb with a BA15d base, which carries two pins, would result in an incompatible fit even if the outer profile is otherwise similar.