Avanti II Back Up Light Bulb Size

The Avanti II back up light uses 1156 and P21W bulb sizes for the lighting components. Provided data covers the specific time range from 1965 through 1973.

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
1965-1973	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 Avanti II uses the 1156 bulb for its back up lights across all listed model years, spanning 1965-1973.
The 1156 is an ANSI-standardized bulb type, meaning its physical and electrical specifications are governed by a recognized North American standard shared across the US and Canada.
This bulb operates on a 12-volt electrical system, which was the standard automotive voltage adopted widely by manufacturers during this era.
At 21 watts, the 1156 produces a relatively high output for a single-filament incandescent bulb, a characteristic that suits its role in back up lighting where visibility behind the vehicle is a functional priority.
The 1156 uses a BA15s bayonet base, where "BA15s" denotes a single-contact bayonet fitting with a 15mm base width, distinguishing it from double-contact variants such as the BA15d.
Because the 1156 is single-filament, it serves only one lighting function per socket, unlike dual-filament bulbs that can handle two functions such as braking and running lights simultaneously.
The BA15s base type is not universally interchangeable with other bayonet bases; substituting a double-contact base bulb into a single-contact socket is not compatible, even when the outer housing appears similar.