Cadillac Series 75 Fleetwood Back Up Light Bulb Size

The Cadillac Series 75 Fleetwood back up light utilizes 1073 and P21W bulb sizes for illumination. Available data for the specified lighting components covers the range from 1953 to 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
1964	P21W
1962-1963	1073
1960-1961	P21W
1959	1073
1958	P21W
1953-1957	1073

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Lower wattage variant of 1156. 12V, 13W.	1073

Other Locations

Additional Notes

The back up light bulb specifications for the Cadillac Series 75 Fleetwood span model years 1953 through 1964, with two distinct bulb types appearing across that range: the P21W and the 1073.
The 1073 bulb is the more frequently specified of the two, covering the 1953-1957, 1959, 1962, and 1963 model years.
The 1073 follows the ANSI standard used in the United States and Canada, operating at 12 volts with a rated output of 13 watts through a single filament.
The P21W is specified for the 1958, 1960-1961, and 1964 model years, and follows the ECE standard used in Europe and worldwide markets.
The P21W operates at 12 volts with a rated output of 21 watts, making it a higher-wattage single-filament bulb compared to the 1073.
Both the P21W and the 1073 share the BA15s bayonet base configuration, meaning the physical mounting interface is identical between the two bulb types.
Despite the shared BA15s base, the wattage difference between the two bulbs is significant. The P21W draws 21 watts while the 1073 draws 13 watts, and substituting one for the other may affect circuit load and light output.
The alternating use of P21W and 1073 across consecutive model years indicates that the two bulb types are not treated as interchangeable within these factory specifications.