The Audi 80 front turn signal requires a P21/5W bulb size while the rear turn signal uses a P21W bulb size. Replacement bulb specifications in the chart cover 1988 to 1992 vehicle production years.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Audi 80 uses two distinct bulb types across its turn signal positions for the 1988-1992 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 P21W is a single-filament bulb rated at 12V at 21W, mounted on a BA15s bayonet base.
Both bulb types conform to ECE standards, meaning they are specified for European and worldwide automotive applications.
The BAY15d base of the P21/5W features offset pins to ensure correct orientation, which prevents the two filaments from being wired incorrectly during installation.
The BA15s base of the P21W uses a single-contact design consistent with its single-filament construction, and it is not interchangeable with the BAY15d base used by the P21/5W.
Because the front position requires a dual-filament P21/5W and the rear requires a single-filament P21W, the two bulb types serve different electrical functions and are not substitutes for one another.
The shared 21W output rating between the P21/5W and P21W reflects a common signalling brightness standard, though the differing base types physically prevent cross-position substitution.