The Jaguar XK8 brake light uses P21/5W and P21W bulb sizes according to the provided specifications for the vehicle lighting system. Data for the specific components covers the range from 1997 to 2006.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Jaguar XK8 brake light circuit uses two distinct bulb types across its production run: the dual-filament P21/5W for model years 2000-2006 and the single-filament P21W for model years 1997-1999.
The P21/5W operates at 12V and carries a BAY15d bayonet base, which features offset pins to prevent incorrect installation. Its dual-filament design serves both the brake and tail light functions within a single bulb.
The P21W also operates at 12V but uses a BA15s bayonet base, which has a single contact pin. This base is not interchangeable with the BAY15d base used by the P21/5W, making the two bulb types physically incompatible with each other despite their similar appearance.
Both the P21/5W and P21W conform to ECE standards, meaning they are rated and tested under European and international regulatory frameworks rather than SAE standards common in North American automotive applications.
The Jaguar XK8 (2000-2006) shifted from the single-filament P21W to the dual-filament P21/5W for the main brake light position, reflecting a change in the lamp assembly design between those model year groups.
The Center High Mount Stop Light on the XK8 uses the 12961, a Philips-designated T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12V and 5W. This bulb type is significantly lower in wattage than the main brake bulbs.
The W2.1x9.5d wedge base of the 12961 is a push-fit design with no bayonet or screw mechanism, and it is not interchangeable with the BA15s or BAY15d bases used elsewhere in the XK8 brake light system.
The 12961 designation is a Philips part number rather than an industry-standard ECE or SAE code. Equivalent bulbs from other manufacturers are typically cross-referenced by their T10 form factor and W2.1x9.5d base specification.