Mercury Monarch Map Light Bulb Size

The Mercury Monarch map light utilizes 1003 and 211-2 bulb sizes for the interior illumination system. Data for the specified lighting components covers the period from 1975 through 1980.

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
1980	211-2
1975-1979	1003

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Festoon bulb, 41mm length, SV8.5 base. 12V, 12W.	211-2
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1003

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Additional Notes

The 1003 bulb is the map light specification for the Mercury Monarch across the 1975-1979 model years, making it the predominant bulb type within this fitment range.
The 1003 is a single-filament bulb rated at 12 volts and 21 watts, fitted with a BA15s bayonet base. The BA15s designation indicates a single-contact bayonet cap with a 15mm base width.
The 211-2 bulb is specified for the 1980 Mercury Monarch map light, representing a distinct departure from the bulb type used in prior model years.
The 211-2 is a festoon-style bulb rated at 12 volts and 12 watts, measuring 41mm in length with an SV8.5 base. Festoon bulbs seat by compression between two contact points rather than using a socket base.
The wattage difference between the two bulb types is notable. The 1003 draws 21 watts while the 211-2 draws 12 watts, meaning the two types are not electrically equivalent and are not interchangeable.
Both the 1003 and 211-2 carry ANSI standardization applicable to the United States and Canada, indicating conformance to a defined set of dimensional and electrical tolerances.
The base types of the two bulbs are physically incompatible. The BA15s bayonet base of the 1003 and the SV8.5 festoon base of the 211-2 require different socket configurations, which prevents cross-year substitution.