The Scion xB brake light requires a 7443 bulb size for proper installation and function within the rear lighting assembly. Provided information covers a span of time starting in 2004 and ending in 2015.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 7443 bulb is the dominant brake bulb type across the Scion xB, covering the outer brake position for the 2004-2006 and 2008-2015 model years.
The 7443 is a dual-filament wedge bulb following the T20 form factor, rated at 12V with a 21W high filament and a 5W low filament, conforming to ANSI standards used in the US and Canada.
The dual-filament design of the 7443 allows it to serve both a bright brake signal and a dimmer running light function within a single bulb housing.
The Scion xB (2004-2006) uses a 921 bulb for the center high mount stop light, a position that is separate from the outer brake lights on those model years.
The 921 is a single-filament T15 wedge bulb rated at 12V and 16W, also conforming to ANSI standards for the US and Canadian markets.
The T15 and T20 designations refer to the wedge base width of each bulb type, and the two are not interchangeable despite sharing a similar wedge form factor.
The 7443 and 921 operate on the same 12V electrical system but differ in filament count, wattage, and base size, making substitution between the two incompatible for the xB's brake lighting positions.