Ford Prefect Dome Light Bulb Size

The Ford Prefect dome light uses bulb sizes 1003 and 63 according to the provided specifications for the interior lighting components. The data covers the range from 1950 to 1957.

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
1956-1957	1003
1950-1955	63

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1003
ANSI standard (US & Canada). Single-filament bulb with BA9s base. 12V, 0.63W.	63

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Additional Notes

The Ford Prefect dome light specifications cover model years 1950 through 1957, with two distinct bulb types used across that span.
The bulb 63 is the more frequently specified type, appearing in the Ford Prefect across six model years from 1950 to 1955.
The 63 bulb is an ANSI-standard single-filament type rated at 12V and 0.63W, fitted with a BA9s bayonet base, which is a miniature bayonet cap smaller than the more common BA15s format.
The 1003 bulb replaces the 63 in the 1956-1957 model years, representing a shift to a higher-wattage unit within the same 12V electrical system.
The 1003 bulb is also an ANSI-standard single-filament type, rated at 12V and 21W, and uses a BA15s bayonet base, which is physically larger than the BA9s base of the 63 bulb.
Because the BA9s and BA15s bases are different sizes, the 63 and 1003 bulbs are not interchangeable, and substituting one for the other in the Ford Prefect dome light socket is not possible without modification.
The wattage difference between the two bulbs is substantial, with the 1003 drawing 21W compared to the 0.63W of the 63 bulb, reflecting a significant difference in light output between the earlier and later model years.
Both bulb types conform to ANSI standards applicable in the United States and Canada.