Buick GS Back Up Light Bulb Size

The Buick GS back up light requires a 1156 bulb size for the specific lighting components located at the rear of the vehicle. Data for the bulb specifications 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 across all three model years covered in the Buick GS back up light specifications, spanning 1970-1972.
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 standards shared across those markets.
It operates on a 12-volt system at 21 watts, which is consistent with the standard automotive electrical architecture of that era.
The 1156 uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin, as opposed to the dual-pin BA15d variant. This base type is not interchangeable with double-contact bayonet sockets.
As a single-filament bulb, the 1156 serves one dedicated function per socket. This distinguishes it from dual-filament types such as the 1157, which handle two functions, such as braking and running light, within a single housing.
The BA15s base of the 1156 is physically similar in shell size to the BA15d, but the pin offset differs. Substituting a double-contact bulb into a single-contact socket is not supported by these specifications.