The Volkswagen Fox brake light requires a P21W bulb size for proper installation and function within the rear lighting assembly. Data for the specified component covers the period from 1987 through 1993.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Volkswagen Fox uses the P21W bulb for the brake light position across the 1987-1993 model years.
The P21W is an ECE-standard single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, a base type common in European and international automotive lighting applications.
The BA15s bayonet base is a single-contact design, which is a relevant fitment detail given that a visually similar double-contact variant, the BA15d, exists and is not interchangeable with it.
The center high mount stop light on the Volkswagen Fox uses the 12961 bulb across the same 1987-1993 model years.
The 12961 is a Philips part number designating a miniature wedge bulb of the T10 type, rated at 12V and 5W, with a W2.1x9.5d wedge base.
The W2.1x9.5d base is a wedgeless push-in type, meaning it is retained by the socket itself rather than by a locking mechanism, and it is not compatible with bayonet or screw-base sockets.
The two bulb types used in the Fox brake lighting system, the P21W and the 12961, differ substantially in wattage, with the P21W rated at 21W and the 12961 rated at 5W, reflecting their distinct roles in primary brake signalling versus the supplemental high mount stop light.
The P21W and 12961 use entirely different base types and are not interchangeable with each other or with bulbs outside their respective base families.