BMW 320i Turn Signal Bulb Size

Additional Notes

• The P21W bulb is the most consistently used type across the BMW 320i's turn signal specifications, serving as the rear turn signal bulb from 1977-1983 and again in 2013-2015. It follows the ECE standard and operates as a single-filament signalling bulb with a BA15s bayonet base at 12V and 21W.
• The P21/5W bulb appears in the front turn signal position on the BMW 320i from 1977-1983. Unlike the P21W, it carries a dual-filament design rated at 21W and 5W, uses a BAY15d bayonet base, and also conforms to the ECE standard.
• The BAY15d base of the P21/5W and the BA15s base of the P21W are not interchangeable. The BAY15d base has offset pins to accommodate the dual-filament design, while the BA15s base has symmetrical pins for single-filament use.
• The 2017-2018 front turn signal position on the BMW 320i with Halogen Capsule Headlamps uses the 3457NA bulb, an ANSI-standard dual-filament wedge type in a T25 form factor with natural amber glass, rated at 12V and 27W/7W.
• The 2016 front turn signal with Halogen Capsule Headlamps uses the 3357NA, which shares the T25 wedge form factor and natural amber glass of the 3457NA but is a single-filament bulb rated at 27W, making the two types functionally distinct despite their similar designations.
• The 3457NA and 3357NA are ANSI-standard bulbs primarily used in North American markets, while the PY21W and P21W follow the ECE standard used in European and worldwide markets. This distinction reflects differing regional lighting regulations rather than a difference in vehicle hardware alone.
• The PY21W, used in the front turn signal position for the 2013 and 2015 model years, features a BAU15s bayonet base. The offset pin configuration of the BAU15s is specific to amber-designated sockets and prevents substitution with standard BA15s or BAY15d base bulbs.
• The 2014 front turn signal uses the 12496, a Philips/Osram part number designation for a 12V halogen bulb in a specialty application. Unlike the other bulbs in these specifications, it is identified by a manufacturer part number rather than an ANSI or ECE standard designation.
• The front turn signal position on the BMW 320i shows variation across model years, with at least five distinct bulb types specified between 1977 and 2018. The rear turn signal position, by contrast, uses only the P21W across all years listed.
• The Halogen Capsule Headlamps condition noted for the 2016-2018 front turn signal entries indicates that the 3357NA and 3457NA fitments are specific to that headlamp configuration, meaning vehicles with a different headlamp type in those years may not share the same front turn signal bulb requirement.