Mercury Montclair Map Light Bulb Size

The Mercury Montclair map light requires bulb sizes 1816, 631, 1895, and 81 depending on the specific application. Available information covers a span from 1955 through 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	1816
1967	631
1966	1816
1964-1965	1895
1955	81

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. Variant of 1156. 12V, 21W.	631
ANSI standard (US & Canada). Miniature wedge bulb (T5). 12V, 0.9W.	1895
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 8W.	81

Other Locations

Additional Notes

The Mercury Montclair map light specifications span model years 1955 and 1964-1968, drawing from four distinct ANSI-standard bulb types across those years.
The 1816 bulb, used in the Mercury Montclair for 1966 and 1968, is a miniature wedge bulb of the T3.25 form factor, rated at 12V and 4W. Its wedge base design means it requires no separate socket hardware, as the base of the glass envelope itself acts as the retaining element.
The 1895 bulb, fitted to the 1964-1965 Montclair, is also a miniature wedge type, though it follows the smaller T5 form factor and draws only 0.9W at 12V, making it among the lowest-wattage bulbs in these specifications.
Although both the 1816 and 1895 are miniature wedge bulbs, their differing T3.25 and T5 form factors mean they are not interchangeable despite sharing the same base style and voltage rating.
The 631 bulb, specified for the 1967 Montclair, uses a BA15s single-contact bayonet base and is rated at 12V and 21W. At 21W, it draws considerably more power than the other map light bulbs listed across these model years.
The 631 is described as a variant of the 1156 bulb. While both share the BA15s bayonet base, substitution between them would depend on whether the wattage and physical envelope of the specific variant are compatible with the fixture.
The 81 bulb, specified for the 1955 Montclair, also uses a BA15s single-contact bayonet base and is rated at 12V and 8W. It shares its base type with the 631 but differs in wattage and is a distinct ANSI type.
Because the 81 and 631 share a BA15s bayonet base, physical fitment in the socket may be possible between them, but their wattage ratings of 8W and 21W respectively represent a significant difference that affects thermal load and circuit compatibility.
All four bulb types in these specifications conform to ANSI standards applicable in both the United States and Canada, indicating a standardized electrical and physical classification system governs their ratings.
The map light bulb type for the Mercury Montclair changed across nearly every model year represented in the specifications, with no single bulb type used across more than two of the listed years.