Cadillac Series 75 Fleetwood Dome Light Bulb Size

The Cadillac Series 75 Fleetwood dome light uses bulb sizes 90 and 1004 depending on the specific application. Data for the 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
1963-1964	1004
1961-1962	90
1960	1004
1959	90
1953-1958	1004

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. Variant of 1157. 12V, 21/5W.	1004
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 13W.	90

Other Locations

Additional Notes

The bulb 1004 is an ANSI-standardized, dual-filament bulb rated at 12V and 21/5W, fitted with a BAY15d bayonet base. It is a variant of the more widely recognized 1157 bulb.
The bulb 90 is an ANSI-standardized, single-filament bulb rated at 12V and 13W, fitted with a BA15s bayonet base.
The BAY15d base used by the 1004 features two offset pins at different heights, which physically prevents it from being seated in a BA15s socket. This means the 1004 and the 90 are not interchangeable despite both using bayonet-style bases.
The Cadillac Series 75 Fleetwood uses the 1004 bulb for the dome light across the 1953-1958 model years, as well as in 1960 and 1963-1964.
The bulb 90 is specified for the dome light in the 1959, 1961, and 1962 model years.
Because the 1004 is a dual-filament bulb and the 90 is single-filament, the two types serve different circuit configurations. Installing one in place of the other would result in either an incomplete circuit or incorrect wattage draw.
The 1004 draws 21W on its primary filament and 5W on its secondary filament, while the 90 draws a fixed 13W from its single filament, reflecting a meaningful difference in light output between the two bulb types.
Both the 1004 and the 90 conform to ANSI standards applicable in the United States and Canada, meaning physical and electrical specifications are governed by a recognized industry standard rather than a proprietary format.