Mercedes-Benz 300TD front turn signal bulbs use P21/5W size while rear turn signal bulbs use P21W size. The replacement chart covers vehicle production spanning 1979 to 1987 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 300TD uses two distinct bulb types across its front and rear turn signal positions: the P21/5W for the front and the P21W for the rear, both conforming to ECE standards used in Europe and worldwide markets.
The P21/5W is a dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base. The dual-filament design allows a single bulb to serve two lighting functions simultaneously.
The P21W is a single-filament bulb rated at 12V and 21W, mounted on a BA15s bayonet base. Its single-filament construction is suited to dedicated turn signal applications that require no secondary function.
The BAY15d base of the P21/5W and the BA15s base of the P21W are not interchangeable. The BAY15d base features offset pins to ensure correct orientation of the dual filaments, while the BA15s base uses a single-contact design with symmetrical pins.
Substituting a P21W in place of a P21/5W front position would result in the loss of the secondary 5W filament function, as the single-filament P21W does not replicate the full output of the dual-filament P21/5W.
The front turn signal position of the Mercedes-Benz 300TD calls for the P21/5W across all model years from 1979-1987, with the exception of 1986, which is not present in the specifications.
The rear turn signal position of the Mercedes-Benz 300TD specifies the P21W across all model years from 1979-1987, with the same gap at 1986 reflected in the data.
Both the P21/5W and P21W operate on a 12V electrical system, consistent with the standard automotive voltage architecture used in the 300TD.