BMW Z3 front inner and rear turn signal bulbs use P21W size, while front outer signals require 12821 bulbs and front turn signals use P21/5W or 2357NA sizes. The replacement chart covers 1996 to 1998 model years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The P21W is the most frequently specified bulb across the BMW Z3 turn signal positions, appearing in the front inner turn signal and rear turn signal positions for the 1996-1998 model years. It is an ECE-standard single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base.
The front outer turn signal on the BMW Z3 uses the 12821 across the 1996-1998 model years. This is a Philips part number designating a miniature T10 wedge bulb with a W2.1x9.5d base, rated at 12V and 5W, making it considerably lower in wattage than the other turn signal bulbs in this application.
The front turn signal position shows a bulb change between model years. The 1996-1997 models use the 2357NA, while the 1998 model uses the P21/5W. Both are dual-filament bulbs sharing the BAY15d bayonet base, but they are not interchangeable without consideration of their differing electrical ratings.
The 2357NA is an ANSI-standard bulb with natural amber glass, rated at 12V with filaments drawing 26.9W and 8W. Its amber glass produces color at the bulb itself rather than relying on a colored lens.
The P21/5W is an ECE-standard dual-filament bulb rated at 12V, with filaments rated at 21W and 5W. Its BAY15d base is physically identical to that of the 2357NA, but the wattage ratings differ significantly between the two bulbs.
The BA15s base on the P21W and the BAY15d base on the P21/5W and 2357NA are not interchangeable. The BAY15d base has offset pins to prevent incorrect installation of dual-filament bulbs in single-filament sockets.
The ECE-standard bulbs (P21W and P21/5W) and the ANSI-standard 2357NA reflect two separate regulatory frameworks. ECE standards are used in Europe and most of the world, while ANSI standards apply in the United States and Canada, which is relevant to the Z3 given its sale in multiple markets.