Ford Mainline Dome Light Bulb Size

The Ford Mainline dome light uses bulb size 1003 and bulb size 63 for interior illumination. Data for the provided bulb sizes covers the range from 1952 to 1956.

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	1003
1952-1955	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

Other Locations

Additional Notes

The Ford Mainline uses two distinct bulb types across its dome light specifications: the 1003 and the 63, both of which are ANSI-standardized bulbs rated for use in the US and Canada.
The 1003 bulb is a single-filament type operating at 12V and 21W, fitted with a BA15s bayonet base. The BA15s designation indicates a single-contact bayonet cap with a 15mm base width.
The 63 bulb is also a single-filament type operating at 12V, but at a significantly lower 0.63W output. It uses a BA9s base, which is a miniature bayonet cap with a 9mm base width.
The BA15s base of the 1003 and the BA9s base of the 63 are physically incompatible with each other, meaning the two bulb types are not interchangeable despite both using bayonet-style fittings.
The Ford Mainline (1952-1955) takes the 63 bulb for the dome light across all four of those model years.
The 1956 Ford Mainline uses the 1003 bulb, which draws considerably more wattage than the 63 used in prior model years.