The Mercedes-Benz 190D uses a P21/5W bulb size for the front turn signal and a P21W bulb size for the rear turn signal. The replacement chart covers 1984 to 1989 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 190D uses two distinct bulb types across its front and rear turn signal positions for the 1984-1989 model years: P21/5W at the front and P21W at the rear.
The P21/5W is a dual-filament bulb rated at 12V with a 21W primary filament and a 5W secondary filament, mounted on a BAY15d bayonet base.
The BAY15d base features two offset pins, a design that prevents incorrect insertion by ensuring the dual filaments are seated in the correct orientation within the housing.
The P21W is a single-filament bulb rated at 12V and 21W, mounted on a BA15s bayonet base, which uses a single pin and is not interchangeable with the BAY15d base used by the P21/5W.
Both bulb types conform to ECE standards, meaning they are recognized for road use across Europe and other markets that follow ECE lighting regulations.
The P21/5W and P21W share the same 21W primary output, but the physical base types differ, making the two bulbs mechanically incompatible with each other's sockets despite the similar wattage rating.
The front turn signal position on the 190D requires the P21/5W specifically because the dual-filament design allows a single bulb to serve more than one lighting function within the same housing.
The rear turn signal position uses the P21W, a single-filament type, indicating that the rear housing is dedicated solely to the turn signal function without a shared secondary role.