Pontiac Grandville Back Up Light Bulb Size

The Pontiac Grandville back up light utilizes 1156, 1157, and P21W bulb sizes depending on the specific version of the vehicle. Data for the provided specifications covers the period from 1971 through 1975.

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
1974-1975	1156
1973	1157
1971-1972	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 the most frequently specified back up light bulb for the Pontiac Grandville, covering the 1971-1972 and 1974-1975 model years.
The 1156 is a single-filament bulb operating at 12 volts and 21 watts, fitted with a BA15s bayonet base, and recognized under ANSI standards in both the United States and Canada.
The 1157 bulb is specified for the 1973 Pontiac Grandville back up light position.
The 1157 is a dual-filament bulb rated at 12 volts with two wattage outputs of 21W and 5W, and it uses a BAY15d bayonet base, also an ANSI-standard part in the US and Canada.
Although both the 1156 and 1157 share a 12-volt, 21-watt primary rating, their base types differ: the BA15s base of the 1156 has a single contact pin, while the BAY15d base of the 1157 has two offset pins to accommodate its dual-filament design.
The physical difference in base configuration between the 1156 and 1157 means the two bulb types are not interchangeable, despite their shared primary wattage rating.