Pontiac Astre Back Up Light Bulb Size

The Pontiac Astre back up light requires bulb size 1156 or 1157 depending on the specific version of the vehicle. Data for the bulb sizes covers the range from 1975 to 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
1977	1156
1975-1976	1157

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 and 1157 are both ANSI-standardized bulb types used in the United States and Canada, and both operate at 12 volts.
The 1156 is a single-filament bulb rated at 21W, fitted with a BA15s bayonet base. The single-contact base accepts only one filament connection, making it suitable for functions requiring a single light output level.
The 1157 is a dual-filament bulb rated at 21W and 5W, fitted with a BAY15d bayonet base. The dual-contact base supports two separate filaments, allowing two distinct brightness levels from a single bulb.
The Pontiac Astre used the 1157 bulb for the back up light in the 1975-1976 model years.
The 1977 Pontiac Astre shifted to the 1156 bulb for the back up light, a change from the dual-filament 1157 used in prior years.
The 1156 and 1157 are not directly interchangeable. Their bayonet bases differ in pin configuration: the BA15s has a single contact pin, while the BAY15d has two offset contact pins. A 1157 socket will not correctly seat a 1156 bulb, and vice versa.