The Mercedes-Benz 400E brake light utilizes a P21W bulb size for the rear lighting system. Data for the specific component covers the range from 1992 through 1993.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The P21W is the sole bulb type specified across all brake light positions on the Mercedes-Benz 400E, covering both the standard brake lights and the center high mount stop light for the 1992-1993 model years.
The P21W follows the ECE (Economic Commission for Europe) standard, a regulatory framework adopted across Europe and numerous other markets worldwide, governing bulb performance and construction requirements.
As a single-filament bulb, the P21W is dedicated to one lighting function only. This contrasts with dual-filament types, which serve two functions such as combined stop and tail light duties from a single bulb.
The P21W operates at 12 volts and consumes 21 watts, which is a standard output level for signalling and stop light applications in passenger vehicles.
The BA15s designation refers to a single-contact bayonet base with a 15mm collar. The single-contact design is a direct consequence of the single-filament construction, as only one electrical circuit is required.
The BA15s base is distinct from the BA15d base, which carries two contacts for dual-filament bulbs. Substituting a BA15d bulb into a BA15s socket is not mechanically compatible, as the pin and contact configurations differ.