The Mercedes-Benz CLK63 AMG inner tail light uses a P21/4W bulb size while the outer tail light requires a P21/5W bulb size. The replacement chart covers 2007 to 2008 model years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercedes-Benz CLK63 AMG uses two distinct bulb types across its tail light assembly for the 2007-2008 model years: the P21/4W in the inner tail light position and the P21/5W in the outer tail light position.
Both the P21/4W and P21/5W are dual-filament bulbs, meaning each contains two separate filaments within a single envelope, allowing one bulb to serve two lighting functions simultaneously.
The P21/4W operates at 12 volts with filament ratings of 21W and 4W, while the P21/5W operates at 12 volts with filament ratings of 21W and 5W. The higher-wattage filament in both types typically handles braking or turn signal functions, while the lower-wattage filament handles running light functions.
Although the P21/4W and P21/5W share a similar naming convention and voltage rating, they are not interchangeable. Each uses a different bayonet base design to prevent incorrect installation.
The P21/4W uses a BAZ15d bayonet base, which features offset pins at the base of the bulb. This offset configuration is specific to the BAZ15d standard and physically prevents the bulb from seating into a socket designed for a different base type.
The P21/5W uses a BAY15d bayonet base, which also features offset pins but with a different pin spacing than the BAZ15d. This distinction ensures the outer tail light socket accepts only the correct bulb type.
Both bulb types conform to ECE standards, a regulatory framework recognized across Europe and numerous other markets worldwide, governing performance and safety requirements for automotive lighting components.