Ford E-450 Super Duty Back Up Light Bulb Size

Additional Notes

• The Ford E-450 Super Duty back up light specifications reference three distinct ANSI-standard bulb types across its model years: the 3156, 2456, and 2356.
• The 3156 is a single-filament wedge bulb in a T25 form factor, rated at 12V and 27W. Its wedge base design means it is inserted directly into a socket without a separate locking mechanism.
• The 2356 uses a BAY15d bayonet base and carries dual filaments, also operating at 12V. The BAY15d base features two offset pins, which physically prevents incorrect installation of a single-filament substitute in the same socket.
• The 2456 is a festoon-style bulb rated at 12V and is designated for specialty applications. Festoon bulbs are cylindrical in shape and are held in place by spring-loaded end caps rather than a base socket.
• The 3156 is the most frequently specified bulb across the Ford E-450 Super Duty back up light data, appearing in model years 2000, 2005, 2008, and 2014-2023.
• The 2356 and 3156 are not interchangeable despite both operating at 12V. The 2356 uses a BAY15d bayonet base while the 3156 uses a wedge base, making the two physically incompatible with each other's sockets.
• The 2456 festoon bulb also cannot substitute for either the 3156 or the 2356, as its end-cap mounting format is mechanically distinct from both wedge and bayonet socket types.
• Model years 2001-2004, 2006, and 2010 share the 2356 dual-filament bayonet bulb, while 2007, 2009, and 2011-2013 share the 2456 festoon bulb, indicating that the same physical socket configuration was carried across those respective production spans.