The BMW 850i uses P21W bulbs for both front and rear turn signal applications, with this bulb size remaining consistent across the model line. The replacement chart covers 1993 to 1997 model years and details the bulb specifications for turn signal fixtures throughout the vehicle's production span.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The BMW 850i uses the P21W bulb for both front and rear turn signals across the 1993-1997 model years.
The P21W is an ECE-standardized bulb type, meaning it conforms to European and international automotive lighting regulations rather than SAE standards used in North American markets.
P21W bulbs operate on a 12-volt electrical system and draw 21 watts, which is the standard wattage for single-filament turn signal applications.
The P21W uses a BA15s bayonet base, where "BA" denotes a bayonet-style mount, "15" refers to the 15mm base width, and the lowercase "s" indicates a single contact at the base.
Because the P21W is single-filament, it serves a dedicated signalling function and is not shared with braking or running light circuits, unlike dual-filament bulbs such as the P21/5W.
The BA15s base is not interchangeable with the BA15d base, which carries two contacts. Substituting a BA15d bulb into a BA15s socket is not possible without modification.
The uniform use of P21W across all five model years and both front and rear positions means a single bulb type covers all turn signal positions on the 850i throughout its listed production span.