Jaguar XJ12 Back Up Light Bulb Size

The Jaguar XJ12 back up light requires a P21W bulb size for proper installation and function. Data for the specific component covers the period from 1978 through 1996.

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
1994-1996	P21W
1978-1979	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 P21W is the sole bulb type listed across all back up light specifications for the Jaguar XJ12, covering model years 1994-1996, 1979, and 1978.
The P21W is an ECE-standard single-filament bulb, meaning it carries one filament and is rated for signalling functions rather than continuous illumination duties.
The bulb operates at 12 volts with a 21-watt output, which is a standard wattage for single-filament automotive signalling applications.
The P21W uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin offset, distinguishing it from the dual-contact BA15d variant.
The BA15s base is not interchangeable with the BA15d base despite sharing the same 15mm bayonet collar size, as the pin configurations differ.
The ECE designation indicates the P21W conforms to United Nations Economic Commission for Europe regulations, a standard recognized across European and many worldwide markets.
The 1994-1996 Jaguar XJ12 and the 1978-1979 Jaguar XJ12 share the same P21W back up light bulb specification, indicating fitment consistency across those respective production periods.