The Audi S6 tail light utilizes P21W and 12821 bulb sizes for the specific lighting components located at the rear of the vehicle. Data for the specific bulb sizes covers the range from 1995 through 2014.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Audi S6 inner tail light positions for 2007-2011 all use the H21W bulb, an ECE-standard single-filament signalling bulb rated at 12V and 21W with a BAY9s base.
The BAY9s base on the H21W is an offset bayonet fitting, which means it is not interchangeable with bulbs using a standard BA15s bayonet base despite sharing the same 21W power rating.
The Audi S6 outer tail light positions for 2007-2011 use the P21W bulb, an ECE-standard single-filament signalling bulb rated at 12V and 21W with a BA15s bayonet base.
The outer tail light positions for 2013-2014 also use the P21W, as do the outer tail light positions for 2007-2008, placing P21W as the most consistently specified bulb type across the outer tail light positions in these specifications.
Although the H21W and P21W share identical voltage and wattage ratings, their base types differ, making them physically non-interchangeable with each other.
The 1995 Audi S6 outer tail light uses the 12821, a Philips-designated miniature wedge bulb of the T10 form factor with a W2.1x9.5d base, rated at 12V and 5W, which is a significantly lower wattage than the P21W and H21W types used in later model years.
The W2.1x9.5d base on the 12821 is a wedge-style fitting, which is mechanically distinct from the bayonet-style bases found on both the H21W and P21W bulbs.