BMW 328i Turn Signal Bulb Size

Additional Notes

• The P21W is the most consistently used bulb across the BMW 328i turn signal specifications, appearing in the Rear Turn Signal position for 1996-2000 and 2014-2015, as well as the Front Turn Signal for 1999-2000. It is an ECE-standard single-filament signalling bulb rated at 12V and 21W, fitted with a BA15s bayonet base.
• The P21/5W is a dual-filament variant of the P21W family, rated at 12V with a 21W/5W split across its two filaments, and uses a BAY15d bayonet base. On the BMW 328i, it serves the Front Inner Turn Signal and Front Turn Signal positions for 1996-1998, making it distinct from the single-filament P21W despite the similar designation.
• The BAY15d base of the P21/5W and the BA15s base of the P21W are not interchangeable. The BAY15d base has offset pins to prevent incorrect installation of a dual-filament bulb in a single-filament socket, and substituting one for the other in the 328i would result in incorrect fitment.
• The 1997-1998 Front Outer Turn Signal position uses bulb size 12821, a Philips miniature wedge bulb in the T10 form factor with a W2.1x9.5d base, rated at 12V and 5W. This is a significantly lower wattage than the bulbs used in the primary front and rear turn signal positions.
• The 1997-1998 Front Turn Signal specifications include a separate Side position using bulb 12961, also a Philips T10 miniature wedge bulb with a W2.1x9.5d base at 12V and 5W. The 12821 and 12961 share the same base type and electrical ratings, though they carry different Philips part numbers.
• The 2016 Front Turn Signal position specifies the 3357NA, but only for vehicles equipped with halogen capsule headlamps. This bulb is an ANSI-standard single-filament wedge in the T25 form factor with natural amber glass, rated at 12V and 27W, and is specific to the North American market standard.
• The 2015 Front Turn Signal uses the PY21W, an ECE-standard amber single-filament bulb rated at 12V and 21W with a BAU15s bayonet base. The BAU15s base has an offset pin arrangement that differs from both the BA15s and BAY15d bases used in other 328i turn signal positions, preventing cross-substitution.
• The 2014 Front Turn Signal specifies bulb 12496, a Philips or Osram halogen bulb for a specialty application rated at 12V. This bulb occupies the same position as the PY21W in 2015 and the 3357NA in 2016, indicating that the front turn signal fitment changed across those three consecutive model years.
• The 1998 Front Turn Signal specification lists two separate bulbs for the same model year: P21/5W for the front-facing position and 12961 for the side position. This indicates the 1998 328i used a dual-position front turn signal assembly requiring bulbs of different types and wattages within the same lamp unit.
• The rear turn signal specification for the BMW 328i shows no variation in bulb type across all listed years from 1996-2000 and 2014-2015, with the P21W specified throughout. The front turn signal position, by contrast, shows six different bulb specifications across the same span of years.