Acura TL Back Up Light Bulb Size

Additional Notes

• The Acura TL backup light bulb specification calls for one of two bulb types across its model years: the 921 and the 7440, both of which are ANSI-standardized wedge-base bulbs rated at 12 volts.
• The 921 is a T15 wedge bulb rated at 16 watts, and it is the specified backup light bulb for the Acura TL across the 1999-2014 model years, with the exception of 2007 and 2008.
• The 7440 is a T20 single-filament wedge bulb rated at 21 watts, and it is the specified backup light bulb for the Acura TL for the 1995-1998 model years.
• The T15 and T20 designations refer to the outer width of the bulb envelope, with T15 indicating a narrower profile than the T20. These two sizes are physically incompatible with each other's sockets.
• The 7440 draws 21 watts versus the 921's 16 watts, meaning the earlier 1995-1998 Acura TL used a higher-wattage backup light bulb than the later generations.
• Despite the wattage difference, both the 921 and the 7440 share the same 12-volt operating voltage, which is standard across automotive lighting applications.
• The wedge base design used by both bulb types means the bulb is held in its socket by the tension of the base itself rather than by a separate locking mechanism such as a bayonet or screw base.
• The 921 and 7440 are not interchangeable. Substituting one for the other would result in a size mismatch at the socket, regardless of the shared voltage rating.