Mercury Caliente Dome Light Bulb Size

The Mercury Caliente dome light requires bulb size 1816 or 1003 depending on the specific application for the interior lighting system. Data for the bulb sizes covers the range from 1964 to 1967.

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
1967	1816
1964-1966	1003

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Miniature wedge bulb (T3.25). 12V, 4W.	1816
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1003

Other Locations

Additional Notes

The Mercury Caliente uses two distinct bulb types across its model years for the dome light position: the 1003 and the 1816.
The 1003 bulb is a single-filament type with a BA15s bayonet base, rated at 12V and 21W under the ANSI standard applicable to the US and Canada.
The BA15s bayonet base designation indicates a single-contact bayonet fitting with a 15mm base, which is a common but not universal base type and is not interchangeable with double-contact bayonet variants.
The 1816 is a miniature wedge bulb in the T3.25 form factor, rated at 12V and 4W, also conforming to the ANSI standard for the US and Canada.
The T3.25 wedge form factor uses no base pins or bayonet fittings, relying instead on the glass envelope itself to make contact within the socket, making it physically incompatible with bayonet-style sockets.
The 1003 and 1816 bulbs differ substantially in wattage, at 21W and 4W respectively, meaning they are not interchangeable even if a socket were adapted, as the power draw and light output would differ significantly.
The Mercury Caliente (1964-1966) uses the 1003 bulb for the dome light across three consecutive model years.
The 1967 Mercury Caliente shifted to the 1816 bulb, which operates at a considerably lower wattage than the 1003 used in prior years.