Audi 100 Series front turn signal bulbs use a 1157 size, while rear turn signal bulbs accommodate either 1156 or 1157 sizes. The replacement chart covers vehicle production spanning 1969 to 1977 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 Audi 100 Series front turn signal uses the 1157 bulb across all model years from 1969-1977.
The 1157 is a dual-filament bulb operating at 12V with a 21W/5W output, mounted on a BAY15d bayonet base, and standardized under ANSI specifications for the US and Canadian markets.
The BAY15d base features two offset pins at different heights, a physical design that prevents incorrect single-filament bulbs from being seated in a dual-filament socket.
The rear turn signal on the Audi 100 Series shifted from the 1157 bulb in 1969-1971 to the 1156 bulb in 1973-1977.
The 1156 is a single-filament bulb operating at 12V with a 21W output, mounted on a BA15s bayonet base, and also standardized under ANSI specifications for the US and Canadian markets.
The BA15s base used by the 1156 has two pins at equal heights, making it physically incompatible with the BAY15d socket used by the 1157, despite both bulbs sharing the same 15mm base width.
Because the front and rear turn signals on the 1973-1977 Audi 100 Series use different bulb types, the 1157 and 1156 are not interchangeable between those positions on those model years.
The 1157 and 1156 share the same 21W rating on their primary filament, but the 1157 carries an additional 5W secondary filament that the single-filament 1156 does not have.