The Mercedes-Benz SL550 front turn signal bulb size measures PY24WNA or 1156NA, while rear turn signal bulbs measure 12496 or PY21W in size. The replacement chart covers 2007 to 2012 model years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The PY24WNA is an ANSI-standard amber bulb rated at 12V and 24W, fitted with a PGU20-4 base. It serves as the North American market equivalent of the ECE PY24W and appears in the front turn signal position of the Mercedes-Benz SL550 for model years 2009 and 2011-2012.
The 1156NA is an ANSI-standard single-filament bulb with a BA15s bayonet base and natural amber glass, rated at 12V and 21W. It occupies the front turn signal position on the SL550 for model years 2007-2008, predating the switch to the PY24WNA fitment.
The BA15s bayonet base of the 1156NA and the PGU20-4 base of the PY24WNA are physically incompatible, meaning the two front turn signal bulb types used across the SL550 model years are not interchangeable with each other.
The PY21W is an ECE-standard single-filament amber bulb with a BAU15s bayonet base, rated at 12V and 21W. Its ECE classification indicates it is designed for European and worldwide markets rather than the North American ANSI market.
The BAU15s base of the PY21W differs from the BA15s base of the 1156NA. Although both are bayonet-style bases, the offset pin placement on the BAU15s prevents cross-fitment between these two bulb types.
The 12496 is a Philips/Osram part number designation for a 12V halogen bulb intended for specialty applications. It is listed as the rear turn signal bulb for the SL550 across model years 2007-2009 and 2012.
The rear turn signal position of the SL550 shows a divergence in the 2011 model year, where the PY21W is specified rather than the 12496 used in surrounding years. The PY21W and 12496 carry different base types and are not interchangeable.
The front turn signal specifications for the SL550 reflect a distinction between ANSI-standard bulbs, used in North American market vehicles, and the ECE-standard counterparts from which some of those bulbs are derived.