Mercury Caliente Back Up Light Bulb Size

The Mercury Caliente 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 1964 to 1967.

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
1966-1967	P21W
1965	1141
1964	P21W

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 P21W and 1141 bulbs share identical electrical ratings of 12 volts and 21 watts, and both use a BA15s single-contact bayonet base, making them physically and functionally equivalent despite originating from different standardization systems.
The P21W designation follows ECE regulations, a framework developed for European and international automotive lighting standards, while the 1141 designation follows ANSI standards, which govern automotive lighting in the United States and Canada.
Both bulb types are single-filament designs, which is typical for backup light applications where only a steady on/off function is required rather than variable intensity.
The Mercury Caliente used the P21W for the 1964, 1966, and 1967 model years, making it the more frequently specified bulb across the listed production span.
The 1965 Mercury Caliente is the only model year in the specifications to use the ANSI 1141 bulb for the backup light position.
Because the P21W and 1141 share the same BA15s base and identical voltage and wattage ratings, either bulb is technically interchangeable in the socket, though the regional standard of the replacement may differ from the original specification.