Porsche 912 Back Up Light Bulb Size

The Porsche 912 back up light requires bulb size 1156 or P21W depending on the specific version of the vehicle. Information provided covers the range from 1965 through 1976.

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
1976	1156
1965-1969	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 model years of the Porsche 912 back up light specifications.
The 1156 is a single-filament bulb, meaning it serves one lighting function rather than combining two, such as stop and tail duties.
The 1156 operates at 12 volts and 21 watts, placing it in the standard range for incandescent automotive reverse lighting of its era.
The 1156 uses a BA15s bayonet base, which is a single-contact bayonet fitting. The "s" in BA15s denotes a single contact pin, distinguishing it from the dual-contact BA15d base found on other bulb types.
The 1156 conforms to ANSI standards applicable in the United States and Canada, indicating it meets a defined set of dimensional and electrical tolerances for those markets.
The Porsche 912 used the 1156 bulb for its back up lights across the 1965-1969 model years and again in 1976.
The BA15s bayonet base is not interchangeable with the BA15d base. A dual-contact bulb physically fits the socket but will not make correct electrical contact, and a single-contact bulb will not seat properly in a dual-contact socket.
The 1156 is also commonly designated as P21W in European markets, though the ANSI designation applies specifically to the North American specification listed here.