Pontiac Grand LeMans Back Up Light Bulb Size

The Pontiac Grand LeMans back up light utilizes 1156, 1157, and P21W bulb sizes. Data for the specified lighting components covers the period from 1975 through 1981.

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
1981	1156
1980	1157
1975-1979	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. 12V, 21W/5W.	1157

Other Locations

Additional Notes

The 1156 bulb is an ANSI-standardized single-filament bulb operating at 12 volts and 21 watts, fitted with a BA15s bayonet base. It serves as the back up light bulb for the Pontiac Grand LeMans across the 1975-1979 and 1981 model years.
The 1157 bulb shares the same ANSI standardization and 12-volt, 21-watt primary output as the 1156, but it carries a second filament rated at 5 watts, making it a dual-filament bulb. It is specified exclusively for the 1980 Grand LeMans back up light.
The BA15s base of the 1156 and the BAY15d base of the 1157 are physically distinct bayonet fittings. The BA15s has a single contact pin aligned straight across the base, while the BAY15d has two offset pins to accommodate the dual-filament design. These two base types are not interchangeable.
Because the 1156 and 1157 use different base configurations, a 1157 bulb cannot be substituted into a 1975-1979 or 1981 Grand LeMans socket, and a 1156 bulb cannot be substituted into the 1980 socket.
Both bulb types conform to ANSI standards recognized in the United States and Canada, indicating consistent electrical and dimensional specifications across manufacturers producing these bulb numbers.