Cadillac Series 60 Fleetwood Back Up Light Bulb Size

The Cadillac Series 60 Fleetwood back up light utilizes bulb sizes 1156 and P21W along with 1073. Available information covers the specific time range from 1953 through 1964.

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
1960-1964	1156
1959	1073
1958	1156
1953-1957	1073

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Lower wattage variant of 1156. 12V, 13W.	1073

Other Locations

Additional Notes

The Cadillac Series 60 Fleetwood backup light bulb specifications cover model years 1953 through 1964, with two distinct bulb types appearing across that span: the 1156 and the 1073.
The 1156 bulb is a single-filament type rated at 12 volts and 21 watts, fitted with a BA15s bayonet base, and classified under the ANSI standard applicable in the United States and Canada.
The 1073 bulb shares the same BA15s bayonet base and 12-volt operating voltage as the 1156, but draws notably less power at 13 watts, making it the lower-output of the two types used across these model years.
Despite their wattage difference, both the 1156 and 1073 use an identical BA15s bayonet base, which is a single-contact base with a 15mm collar.
The Cadillac Series 60 Fleetwood used the 1073 bulb for the 1953-1957 model years and again for 1959, while the 1156 was specified for 1958 and then continuously for 1960-1964.
The 1959 model year returned to the lower-wattage 1073 specification after the 1958 model year had used the higher-wattage 1156, indicating the two bulb types are not interchangeable as direct factory replacements despite their shared base type.
Although the BA15s base is physically compatible between the 1156 and 1073, substituting one for the other would result in a mismatch with the original wattage specification for that model year.