Harley-Davidson FLHR Road King Brake Bulb Size

Additional Notes

• The Harley-Davidson FLHR Road King uses the 3157 bulb for the brake light position across the 2007-2020 model years.
• The 3157 is a dual-filament bulb, meaning it contains two separate filaments within a single housing to serve two distinct brightness levels from one unit.
• The bulb operates on a 12-volt electrical system and draws 27 watts on the high-intensity filament and 7 watts on the low-intensity filament, which corresponds to brake and running light functions respectively.
• The 3157 follows the ANSI standard, a designation recognized in both the United States and Canada, indicating the bulb meets a defined set of electrical and physical specifications.
• The bulb belongs to the T25 wedge form factor, a classification that describes the shape and base style of the housing rather than a separate compatibility standard.
• The wedge base design of the 3157 means it is retained by friction rather than a bayonet or screw mechanism, which affects how the bulb is seated and removed from its socket.
• The 3157 shares its physical base with related bulbs in the 3000-series family, such as the 3156 and 3057, though those variants differ in filament configuration or wattage and are not direct replacements without verifying electrical compatibility.