The Alfa Romeo 164 uses the 9004 bulb for both high beam and low beam headlights across all available model years, spanning 1991-1995.
The 9004 is a dual-filament halogen bulb, meaning a single bulb contains two separate filaments: one rated at 65W for high beam output and one rated at 45W for low beam output.
Because both the high beam and low beam positions share the same 9004 bulb type, a single bulb design serves the full headlight system on this vehicle.
The 9004 operates on a 12V electrical system, which is standard for passenger vehicles of this era.
The 9004 uses a P29t base, a three-pronged connector that is specific to this bulb family and is not interchangeable with other common base types such as H4 or 9007.
The 9004 is an ANSI-standardized bulb recognized in the United States and Canada, meaning it conforms to defined performance and dimensional standards within those markets.
The 9004 and 9007 bulbs are frequently confused due to their similar appearance, but their wiring configurations differ, making them incompatible despite the physical resemblance of their connectors.