Mercury Medalist Back Up Light Bulb Size

The Mercury Medalist back up light requires bulb size 1141 or P21W depending on the specific version of the vehicle. Data for the bulb sizes covers the range from 1956 to 1958.

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
1958	P21W
1956-1957	1141

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1141

Other Locations

Additional Notes

The Mercury Medalist backup light specifications cover the 1956-1958 model years, with two distinct bulb types appearing across that span.
The 1141 is an ANSI-standard single-filament bulb operating at 12V and 21W, fitted with a BA15s bayonet base, and it serves the 1956 and 1957 Mercury Medalist.
The P21W is an ECE-standard single-filament signalling bulb also rated at 12V and 21W with a BA15s bayonet base, and it serves the 1958 Mercury Medalist.
Despite originating from different standardization bodies, the 1141 and P21W share identical electrical ratings of 12V and 21W as well as the same BA15s bayonet base configuration.
The BA15s base designation indicates a single-contact bayonet fitting with a 15mm collar, which is the standard physical interface for both bulb types listed in these specifications.
The ANSI designation of the 1141 reflects North American standardization, while the ECE designation of the P21W reflects European and broader international standardization, placing the two types under separate regulatory frameworks despite their physical and electrical similarities.
Because the 1141 and P21W share the same base type and electrical ratings, physical fitment between the two is technically compatible, though regulatory or market-region differences exist between the two standards.