Mercury Montego Back Up Light Bulb Size

The Mercury Montego back up light uses bulb sizes 921, P21W, 1156, and 1076 depending on the specific version of the vehicle. Available data covers the range from 1968 through 2007.

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
2005-2007	921
1973-1976	1156
1972	1076
1968-1971	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Variant of 1156. 12V, 8W.	1076

Other Locations

Additional Notes

The Mercury Montego backup light specifications cover model years 1968-1976 and 2005-2007, with three distinct bulb types used across those years: the 921, 1156, and 1076.
The 1156 is the most frequently specified bulb across the Mercury Montego lineup, appearing in the 1968-1976 model years with one exception, and it follows the ANSI standard recognized in both the US and Canada.
The 1156 is a single-filament bulb with a BA15s bayonet base, rated at 12V and 21W, making it a relatively higher-output incandescent compared to the other types listed in these specifications.
The 921 is specified for the 2005-2007 Mercury Montego and is a T15 wedge bulb rated at 12V and 16W. Its wedge base design differs fundamentally from the BA15s bayonet base of the 1156, meaning the two are not interchangeable.
The 1076 is specified exclusively for the 1972 Mercury Montego among all years listed. It shares the BA15s bayonet base with the 1156 but is rated at only 8W, roughly one-third the wattage output.
Because the 1076 is described as a variant of the 1156 and shares the same BA15s bayonet base, physical fitment between the two is possible, but the significant wattage difference means light output would not be equivalent if one were substituted for the other.
All three bulb types in these specifications operate at 12V, consistent with the standard electrical system voltage used in passenger vehicles of both the classic and modern production eras represented here.
The wedge base of the 921 is a self-retaining design that seats directly into a socket without a locking mechanism, whereas the BA15s bayonet base of the 1156 and 1076 requires a push-and-twist motion to lock into place.