Big Dog K-9 high beam and low beam headlight bulbs both utilize a 9003 bulb size. Replacement specifications for this motorcycle model span 2010 through 2011 in the chart.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 9003 is the sole bulb type across all listed positions and years in the Big Dog K-9 specifications, serving both the high beam and low beam headlight functions in 2010-2011.
The 9003 is a dual-filament halogen bulb, meaning a single physical bulb contains two separate filaments: one rated at 60W for high beam output and one at 55W for low beam output.
Operating voltage for the 9003 is 12V, consistent with standard 12-volt automotive electrical systems.
The 9003 uses a P43t base, which is a three-pronged bayonet-style mount. This base type is specific to the 9003 and its international equivalent, the H4, and is not interchangeable with single-filament base types such as H1 or H7.
The 9003 carries an ANSI designation applicable in the United States and Canada, distinguishing it from the H4, which shares identical electrical and physical characteristics but is classified under ECE regulations used in other markets. Despite this regulatory distinction, the two types are widely regarded as functionally interchangeable.