Mercedes-Benz 300SD front turn signal bulbs measure 1034 or P21/5W in size, while rear turn signal bulbs use the P21W size. The replacement chart covers 1978 through 1993 model 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 300SD uses two distinct front turn signal bulb types across its model years: the 1034 for 1992-1993 and the P21/5W for 1978-1985.
The P21/5W is an ECE-standard dual-filament signalling bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base.
The 1034 is an ANSI-standard dual-filament bulb also rated at 12V, 21/5W, and also fitted with a BAY15d bayonet base, making it a North American market equivalent to the P21/5W.
Despite their shared BAY15d base and identical wattage ratings, the 1034 and P21/5W follow different regional standards, ANSI and ECE respectively, and are not formally interchangeable across those standards.
The 1034 is a variant of the widely used 1157 bulb, which is one of the most common dual-filament automotive bulbs in North American applications.
The rear turn signal position uses the P21W across all listed model years, from 1978 through 1993, without variation.
The P21W is a single-filament ECE-standard bulb rated at 12V and 21W, fitted with a BA15s bayonet base, which is a single-contact base distinct from the dual-contact BAY15d base used in the front turn signal bulbs.
Because the rear turn signal P21W uses a BA15s base while the front turn signal bulbs use a BAY15d base, the front and rear turn signal bulbs for the 300SD are not interchangeable with each other.