Mercury Montclair Dome Light Bulb Size

The Mercury Montclair dome light requires bulb sizes 1003, 1816, or 63 depending on the specific application for the vehicle. Data for the bulb sizes covers the range from 1955 to 1968.

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
1968	1003
1967	1816
1964-1966	1003
1956-1960	1003
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). Miniature wedge bulb (T3.25). 12V, 4W.	1816
ANSI standard (US & Canada). Single-filament bulb with BA9s base. 12V, 0.63W.	63

Other Locations

Additional Notes

The 1003 bulb is the most frequently specified dome light bulb across the Mercury Montclair lineup, appearing in model years 1956-1960, 1964-1966, and 1968.
The 1003 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, and is standardized under ANSI specifications for use in the US and Canada.
The BA15s bayonet base designation indicates a single-contact bayonet fitting with a 15mm base, which is a common automotive bulb mount requiring a push-and-twist installation.
The 1967 Mercury Montclair departs from the 1003 specification, using instead the 1816 bulb for its dome light.
The 1816 is a miniature wedge bulb of the T3.25 form factor, rated at 12V and 4W, representing a significantly lower wattage than the 1003 used in surrounding model years.
Because the 1816 uses a wedge base rather than a BA15s bayonet base, it is not directly interchangeable with the 1003 without a compatible socket.
The 1955 Mercury Montclair uses the 63 bulb, which is a single-filament type fitted with a BA9s base, rated at 12V and 0.63W.
The BA9s base on the 63 bulb is physically smaller than the BA15s base on the 1003, making these two bulb types incompatible with each other despite both using bayonet-style mounts.
All three bulb types specified across the Montclair dome light applications, the 1003, 1816, and 63, are ANSI-standardized products intended for the US and Canadian markets.
The wattage range across the three specified bulb types spans from 0.63W for the 63 bulb to 21W for the 1003, reflecting notable differences in light output between model years.