Rolls-Royce Silver Shadow II Back Up Light Bulb Size

The Rolls-Royce Silver Shadow II back up light utilizes a P21W bulb size for illumination purposes. Available data covers the specific range from 1977 through 1980.

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
1977-1980	P21W

Bulb Specifications

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

Other Locations

Additional Notes

The Rolls-Royce Silver Shadow II uses the P21W bulb across all listed model years, spanning 1977-1980, for the back up light position.
The P21W is an ECE-standardized bulb type, meaning it conforms to the Economic Commission for Europe's regulations governing automotive lighting components used throughout Europe and in many markets worldwide.
This bulb operates on a 12-volt electrical system and draws 21 watts, which is characteristic of a single-filament signalling application rather than a high-output illumination role.
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 configuration.
The single-filament design of the P21W means the bulb serves one dedicated function, as opposed to dual-filament variants that handle two lighting functions within a single housing.
The BA15s base is not interchangeable with the BA15d base, which carries two contact pins offset at different heights. Substituting a BA15d bulb in a BA15s socket is not mechanically compatible.
The consistent P21W fitment across all four listed model years indicates that no bulb specification change occurred within the 1977-1980 production span of the Silver Shadow II for this light position.