Lincoln Mark III Dome Light Bulb Size

The Lincoln Mark III dome light requires bulb size 194, 1891, 1003, or 631 depending on the specific application. Data for the listed components covers the period from 1968 through 1971.

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
1971	194
1970	1891
1969	1003
1968	631

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Miniature wedge bulb (T10). 12V, 3.78W.	194
ANSI standard (US & Canada). Miniature wedge bulb (T5). 12V, 2W.	1891
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, 21W.	631

Other Locations

Additional Notes

The Lincoln Mark III dome light draws from four distinct bulb types across its 1968-1971 model years: the 194, 1891, 1003, and 631.
All four bulb types conform to ANSI standards recognized in both the United States and Canada.
The 194 and 1891 are miniature wedge-style bulbs, while the 1003 and 631 use a BA15s bayonet base, making these two groups mechanically incompatible with each other's sockets.
The 194 (T10 wedge) was fitted to the 1971 Lincoln Mark III and operates at 12V with a wattage of 3.78W.
The 1891 is a T5 wedge bulb rated at 12V and 2W, representing the lowest wattage among the four types listed in these specifications.
The 1003 and 631 share the same BA15s bayonet base and identical electrical ratings of 12V and 21W, yet they are not the same bulb and are not listed as interchangeable in these specifications.
The 631 is noted as a variant of the 1156 bulb type, which is a widely used single-filament BA15s automotive bulb, though the 631 and 1156 are distinct part numbers.
The 1003 and 631 each draw 21W, considerably more than the wedge-type 194 and 1891, reflecting a different generation of dome light design used in the 1968 and 1969 model years.