Mercury Comet Map Light Bulb Size

The Mercury Comet Map Light utilizes bulb sizes 1003, 105, 631, 257, and 57 to provide illumination for the interior cabin area of the vehicle. Available data for the specific lighting components spans from 1962 through 1976 for the various configurations listed.

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
1976	1003
1975	105
1974	1003
1968-1969	631
1964-1967	257
1962-1963	57

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 BA15s bayonet base. Variant of 1156. 12V, 13W.	105
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Variant of 1156. 12V, 21W.	631
ANSI standard (US & Canada). Festoon or BA9s base instrument bulb. 12V, 2W.	257
ANSI standard (US & Canada). Single-filament bulb with BA9s base. 12V, 1W.	57

Other Locations

Additional Notes

The Mercury Comet map light specifications span model years 1962 through 1976, covering five distinct bulb sizes across that period.
The 257 bulb is the most frequently specified across these entries, appearing in the 1964-1967 model years. It is an ANSI-standard 12V, 2W instrument bulb fitted with either a festoon or BA9s base.
The 1003 bulb is specified for the 1974 and 1976 Mercury Comet. It is an ANSI-standard single-filament bulb with a BA15s bayonet base, rated at 12V and 21W.
The 631 bulb is specified for the 1968-1969 model years. Like the 1003, it carries a BA15s bayonet base and a 12V, 21W rating, though it is classified as a variant of the 1156 bulb type.
The 105 bulb, specified for the 1975 model year, also uses a BA15s bayonet base but draws less power at 13W. It is likewise classified as a 1156 variant.
The 57 bulb is specified for the 1962-1963 model years. It uses a BA9s base and is rated at 12V and 1W, making it the lowest-wattage bulb in these specifications.
Three of the five bulb types, the 1003, 105, and 631, share the BA15s bayonet base, while the 257 and 57 use the smaller BA9s base. These two base types are not interchangeable.
The 105 and 631 are both listed as variants of the 1156 bulb type and share the BA15s base, though they differ in wattage at 13W and 21W respectively, which affects their interchangeability.
The 1975 model year stands alone in using the 105 bulb, which is distinct from the 1003 used in the adjacent 1974 and 1976 model years despite both using a BA15s base, as their wattage ratings differ.
The shift from the BA9s-based 57 bulb in 1962-1963 to the 257 in 1964 represents a change in base type within the map light application across these model years.