Mitsubishi Sigma Back Up Light Bulb Size

The Mitsubishi Sigma back up light bulb uses a P21W size. The replacement chart covers vehicle production years from 1989 to 1990.

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
1989-1990	P21W

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

The P21W is the specified back up light bulb for the Mitsubishi Sigma across the 1989-1990 model years.
The P21W follows the ECE (Economic Commission for Europe) standard, a regulatory framework adopted across Europe and numerous other markets worldwide.
This bulb operates on a 12-volt electrical system and draws 21 watts, which is typical for single-filament signalling applications.
The P21W uses a BA15s bayonet base, where "BA" denotes a bayonet cap fitting, "15" refers to the 15mm base width, and the lowercase "s" indicates a single contact at the base.
As a single-filament bulb, the P21W is dedicated to one function only, which in this application is the reverse light.
The BA15s base type is distinct from the BA15d (dual-contact) variant; substituting a dual-contact base bulb in place of a single-contact fitting is not compatible and would result in incorrect installation.