Pontiac Ventura Back Up Light Bulb Size

The Pontiac Ventura back up light utilizes 1156, 1157, and P21W bulb sizes for the rear illumination system. Available data for the specified vehicle covers the period from 1960 through 1977.

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
1974-1977	1156
1971-1973	1157
1960-1961	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 Pontiac Ventura backup light specifications span model years 1960-1977, with two distinct bulb types used across that period: the 1156 and the 1157.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, and recognized under ANSI standards in both the United States and Canada.
The 1157 is a dual-filament bulb also rated at 12V but carrying two wattage ratings, 21W and 5W, fitted with a BAY15d bayonet base, and likewise recognized under ANSI standards in both the United States and Canada.
The 1156 and 1157 share the same voltage rating and primary wattage output of 21W, which can make them appear interchangeable at a glance, but their filament count and base configurations are different.
The BA15s base of the 1156 has a single contact pin, while the BAY15d base of the 1157 has two offset contact pins. These base designs are physically incompatible with each other's sockets.
The Pontiac Ventura used the 1156 for model years 1960-1961 and again for 1974-1977, making it the more frequently specified bulb across the listed years.
The 1157 was specified for the Pontiac Ventura during model years 1971-1973.
The dual-filament design of the 1157 means its socket carries separate circuits for each filament, a wiring configuration that is not compatible with the single-circuit socket designed for the 1156.