The Jaguar XJR brake light utilizes P21W and P21/5W bulb sizes depending on the specific version of the vehicle. Available data covers the range from 1995 through 2009.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Jaguar XJR uses two distinct bulb types across its brake light positions: P21W and P21/5W for the main brake lights, and the 12961 for the center high mount stop light.
The P21/5W is a dual-filament ECE-standard bulb rated at 12V with a 21W brake filament and a 5W running light filament, mounted on a BAY15d bayonet base. Its dual-filament design allows it to serve both a stop and a tail light function within a single housing.
The Jaguar XJR (1995-2006) uses the P21/5W for its main brake lights, reflecting the dual-filament requirement across that model range.
From 2007-2009, the main brake light specification changed to the P21W, a single-filament ECE-standard bulb rated at 12V, 21W, with a BA15s bayonet base. The BA15s base is not interchangeable with the BAY15d base used by the P21/5W, as the two offset pins on the BAY15d prevent incorrect installation.
The P21W and P21/5W share the same wattage on their primary filament and both operate on 12V, but they are not interchangeable due to their different base configurations and filament counts.
The center high mount stop light on the Jaguar XJR uses the 12961 across the 1995-2008 model years. This is a Philips part number designating a T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12V and 5W.
The T10 wedge base of the 12961 is a friction-fit design with no bayonet or screw mechanism, making it physically incompatible with the BA15s or BAY15d bases used in the main brake light positions.
The 12961 operates at 5W, significantly lower than the 21W output of the P21W and the primary filament of the P21/5W, consistent with its role in a supplementary stop light rather than a primary brake light assembly.
Both the P21W and P21/5W conform to ECE regulations, meaning they are designed to meet European and international photometric and safety standards for signalling applications.
The base type difference between the 1995-2006 P21/5W (BAY15d) and the 2007-2009 P21W (BA15s) represents a direct fitment incompatibility, and substituting one for the other without a compatible socket would not be possible.