The Mercedes-Benz 500SEC uses a 2357NA bulb of P21/5W size for the front turn signal and a P21W bulb size for the rear turn signal. The replacement chart covers 1984 to 1993 vehicle production 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 Mercedes-Benz 500SEC front turn signal position uses two different bulb types across its model years, while the rear turn signal position uses the same bulb type across all listed years.
The 2357NA and P21/5W bulbs both use a BAY15d bayonet base and operate on 12V, making them dual-filament types. Despite this shared base type, they originate from different standards bodies and carry different wattage ratings.
The 2357NA is an ANSI-standard bulb used in the United States and Canada, rated at 26.9W for its primary filament and 8W for its secondary filament. Its natural amber glass produces the amber signal color without relying on a colored lens or housing.
The P21/5W follows the ECE standard used in Europe and worldwide markets, rated at 21W for its primary filament and 5W for its secondary filament. The lower wattage of both filaments distinguishes it from the 2357NA despite the shared BAY15d base.
The 1993 Mercedes-Benz 500SEC front turn signal takes the 2357NA, while the 1984-1985 model years take the P21/5W. These two bulbs are not interchangeable despite sharing the same base type, as their filament wattages differ significantly.
The P21W is a single-filament ECE-standard bulb rated at 21W, operating on 12V with a BA15s bayonet base. The BA15s base is a single-contact fitting, which is physically distinct from the dual-contact BAY15d base used by both the 2357NA and P21/5W.
Because the rear turn signal uses the P21W with a BA15s base across all listed years, it is not interchangeable with either of the front turn signal bulbs, which both use the dual-contact BAY15d base.
The difference between a BA15s and a BAY15d base is not limited to the number of contacts. The BAY15d also features offset pins that prevent incorrect single-filament bulbs from being seated in dual-filament sockets, serving as a physical fitment safeguard.