Audi 100 Series front and rear side marker bulbs utilize a 1816 bulb size across both positions. The replacement chart contains bulb size specifications for vehicles produced between 1969 and 1977.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Audi 100 Series uses the 1816 bulb across all listed model years for both front and rear side marker positions.
The 1816 is an ANSI-standardized bulb recognized in the United States and Canada, meaning it conforms to a defined set of electrical and physical specifications shared across manufacturers.
The 1816 bulb is a miniature wedge type, classified under the T3.25 designation. The T3.25 designation refers to a tubular bulb with a width of 3.25 eighths of an inch, which is a standard sizing convention in the ANSI bulb nomenclature system.
The wedge base design means the 1816 bulb has no metal screw base or separate connector pins. Instead, the glass envelope itself is pinched at the bottom to form the electrical contact, which seats directly into a wedge-style socket.
The 1816 operates at 12 volts and draws 4 watts, placing it in the low-wattage range typical of marker and indicator applications rather than primary lighting functions.
The front side marker position on the Audi 100 Series uses the 1816 bulb across the 1969-1977 model years.
The rear side marker position uses the same 1816 bulb, with fitment data covering the 1973-1977 model years.
Because both the front and rear side marker positions share the 1816 specification, a single bulb type serves both locations on the vehicle, which simplifies parts sourcing for the overlapping model years.
The wedge base format of the 1816 is not interchangeable with bayonet or screw-base socket types. A socket designed for a bayonet or Edison-style base will not physically accept a wedge bulb without modification.
While the 1816 is ANSI-standardized, substitution with other T3.25 wedge bulbs requires confirmation that voltage and wattage ratings match, as differences in wattage can affect socket heat tolerance and circuit load.