The Mercedes-Benz G500 tail light requires a bulb size of 12821 for the rear lighting assembly. Data for the specified component covers the range from 2002 to 2008.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The outer tail light position on the Mercedes-Benz G500 draws from two distinct bulb types across its model years: the P21/5W and the 12821.
The P21/5W is an ECE-standard dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base. Its dual-filament design allows it to serve two lighting functions within a single housing.
The 12821 is a Philips part number designating a miniature wedge-style T10 bulb with a W2.1x9.5d base, rated at 12V and 5W. As a single-filament wedge bulb, it serves a single lighting function.
The 12821 bulb applies to the G500 outer tail light across the 2002-2008 model years.
The P21/5W applies to the 2007-2008 model years, though with specific fitment conditions attached to each year.
For the 2007 model year, the P21/5W fitment is restricted to vehicles from chassis number X 169954 onward and from production date 12/22/2006 onward, as referenced under ID 144226.
For the 2008 model year, the P21/5W fitment is restricted to vehicles from ID 144226 onward.
The BAY15d base of the P21/5W and the W2.1x9.5d wedge base of the 12821 are physically incompatible with each other, meaning the two bulb types are not interchangeable regardless of shared voltage ratings.
The coexistence of both bulb types within the 2007 and 2008 model years reflects a mid-production specification change rather than a model-year-wide standardization.