American Motors Ambassador Back Up Light Bulb Size

The American Motors Ambassador back up light uses 1156 and P21W bulb sizes depending on the specific production period for the vehicle. Data for the bulb sizes covers the range from 1958 through 1974.

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
1958-1974	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 American Motors Ambassador uses the 1156 bulb for the back up light across all listed model years, spanning 1958-1974.
The 1156 is an ANSI-standardized bulb type, meaning its specifications are governed by a formal industry standard recognized across the United States and Canada.
The 1156 operates on a 12-volt electrical system, which aligns with the standard automotive electrical architecture used in passenger vehicles of this era.
At 21 watts, the 1156 produces a relatively high output for a single-filament bulb, a characteristic that suits its role in back up lighting where visibility is a functional requirement.
The 1156 uses a BA15s bayonet base, where "BA15s" denotes a single-contact bayonet fitting with a 15mm base width. The single-contact design is directly tied to the bulb having only one filament.
Because the 1156 is a single-filament bulb, it serves one dedicated lighting function per socket, as opposed to dual-filament types that combine two functions, such as stop and tail, within a single unit.
The BA15s base is not interchangeable with the BA15d base, which is a dual-contact bayonet fitting used on two-filament bulbs. Substituting one for the other is not physically compatible.
The 1156 is sometimes cross-referenced with the 7506 bulb in certain markets, though fitment should be confirmed against the original ANSI specification before any substitution is made.