Audi Coupe Headlight Bulb Size

Additional Notes

• The 9004 is a dual-filament halogen bulb, meaning a single unit contains two filaments that serve both high beam and low beam functions. This is why the 9004 appears in both the high beam and low beam positions for the 1985-1987 Audi Coupe, as the same bulb handles both lighting modes depending on which filament is activated.
• The 9004 operates at 12 volts with a wattage rating of 65W on the high beam filament and 45W on the low beam filament. It uses a P29t base, which is a single-contact bayonet-style connector specific to this bulb type.
• The H4651, H4652, and H4656 are sealed beam units rather than replaceable bulbs. In a sealed beam design, the reflector, lens, and filament are fused into a single glass unit, and the entire assembly is replaced when the light fails rather than just the bulb.
• All three sealed beam types share a 4x6-inch rectangular form factor and operate at 12 volts. Despite their physical similarity, H4651, H4652, and H4656 are distinct ANSI-designated variants and are not interchangeable without confirming the specific designation required for each position and year.
• For the 1981 and 1984 Audi Coupe, the high beam position uses the H4651 while the low beam position uses the H4652, indicating that two different sealed beam units are fitted to the same vehicle, each designated for its specific function.
• The 1982-1983 Audi Coupe low beam position specifies the H4656, which differs from the H4652 used in 1981 and 1984. Substituting one sealed beam variant for another without matching the correct ANSI designation risks non-compliant light output or fitment issues.
• All bulb and sealed beam types listed across the full 1981-1987 range conform to ANSI standards applicable in the United States and Canada, indicating these specifications are market-specific and may differ from European-market equivalents.
• The transition from sealed beam units to the 9004 halogen bulb between the 1984 and 1985 model years represents a shift in headlight technology, as sealed beam systems integrate all optical components into one unit while the 9004 system allows the bulb alone to be replaced within a separate reflector housing.