The Audi Fox front and rear turn signal bulbs use either 1157 or 1156 size bulbs. The replacement chart covers 1973 to 1979 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 1156 and 1157 are the two bulb types specified for turn signal use across all model years of the Audi Fox covered in these specifications.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, and classified under the ANSI standard used in the United States and Canada.
The 1157 is a dual-filament bulb rated at 12V with filaments drawing 21W and 5W respectively, fitted with a BAY15d bayonet base, and also classified under the same ANSI standard.
The BA15s and BAY15d bayonet bases are physically distinct and not interchangeable. The BAY15d base features offset pins to prevent incorrect installation, while the BA15s base has symmetrically placed pins.
Because the 1156 and 1157 share a similar 15mm bayonet base diameter but differ in pin placement, a 1157 bulb cannot seat correctly in a 1156 socket, and a 1156 bulb installed in a 1157 socket would not engage the second filament circuit.
The Audi Fox front turn signal used the 1156 from 1973-1976 and transitioned to the 1157 for 1977-1979, representing a shift from a single-filament to a dual-filament application at that position.
The rear turn signal of the Audi Fox used the 1156 across 1973-1978, with the 1157 specified only for the 1979 model year at that position.
In 1979, both the front and rear turn signals of the Audi Fox share the same 1157 bulb specification, making that the only model year with a uniform bulb type across both positions.
The dual-filament nature of the 1157 allows a single bulb to serve both a turn signal function and a secondary lower-intensity function, such as a parking or running light, within the same housing.