Jaguar XJS Back Up Light Bulb Size

The Jaguar XJS back up light requires a P21W bulb size for proper installation and function within the rear lighting assembly. Data for the specific bulb requirements covers the range from 1992 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
1992-1996	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 Jaguar XJS uses the P21W bulb for its back up light across the 1992-1996 model years.
The P21W is an ECE-standardized bulb type, meaning it conforms to European and international regulations rather than SAE standards commonly used in North American automotive lighting.
P21W bulbs operate on a 12-volt electrical system and draw 21 watts, which is a typical power rating for single-filament signalling applications such as reverse lights.
The P21W uses a BA15s bayonet base, where "BA15" refers to the 15mm base width and the lowercase "s" denotes a single-contact configuration, distinguishing it from dual-contact variants like the BA15d.
Because the P21W is a single-filament bulb, it serves one lighting function only, which is consistent with its use as a dedicated back up light rather than a combined stop or tail light.
The BA15s bayonet mount is not interchangeable with screw-base or wedge-base bulb types, so substitutions must match the bayonet fitting to seat and make electrical contact correctly.
The P21W designation is shared across many European vehicle manufacturers, which means the bulb itself is widely available, though fitment to a specific housing depends on the socket design of the Jaguar XJS.