Audi 100 Series Back Up Light Bulb Size

The Audi 100 Series back up light utilizes 1156 and P21W bulb sizes for various applications within the lighting system. Data for the specified components covers the range from 1969 to 1977.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1969-1977	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The 1156 is the sole back up light bulb type specified for the Audi 100 Series across all listed model years.
The Audi 100 Series used the 1156 bulb for its back up lights from 1969-1977.
The 1156 is an ANSI-standardized bulb, meaning its physical and electrical specifications conform to a defined industry standard recognized in the United States and Canada.
The 1156 operates on a 12-volt electrical system and draws 21 watts, which is typical for single-filament automotive signal and reverse lighting applications.
The 1156 uses a BA15s bayonet base, a single-contact mount where the bulb is inserted and twisted to lock into the socket.
Because the 1156 is a single-filament bulb, it serves only one lighting function per socket, as opposed to dual-filament types that can handle two functions such as braking and running lights simultaneously.
The BA15s base designation indicates a 15mm bayonet cap with a single contact pin, and substituting a bulb with a different base type such as BA15d would result in an incompatible fit.
The 1156 is sometimes cross-referenced under the designation 7506 in international markets, though fitment should be confirmed against the BA15s base and 21W rating before substitution.