Cadillac Calais Back Up Light Bulb Size

The Cadillac Calais back up light utilizes 1156 and P21W bulb sizes for the rear illumination system. Data for the lighting components spans the period 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
1965-1976	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 Cadillac Calais uses the 1156 bulb for the back up light position across all listed model years from 1965 to 1976.
The 1156 is a single-filament bulb, meaning it serves one lighting function rather than combining two, such as stop and tail, into a single unit.
The 1156 operates at 12 volts and 21 watts, which is consistent with standard automotive electrical systems of that era.
The 1156 uses a BA15s bayonet base, where "BA15s" denotes a single-contact bayonet fitting with a 15mm base width.
The 1156 is an ANSI-standardized bulb recognized in both the United States and Canada, placing it within a widely adopted North American specification framework.
Because the 1156 is a single-filament type, it is not interchangeable with the visually similar 1157, which carries a dual-filament design and a different pin configuration despite sharing the same bayonet base style.