Ford F-550 Super Duty Back Up Light Bulb Size

The Ford F-550 Super Duty back up light utilizes bulb sizes WT21W, 3157, 7440, 921, 2356, 2456, and 3156. Available information covers a time range from 1999 to 2022.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
2020-2022	WT21W
2019	3157
2017-2018	7440
2011-2016	921
2009-2010	2356
2008	2456
2007	921
2006	2356
2003-2005	2456
2002	2356
2001	3156
2000	2456
1999	3156

Bulb Specifications

Description	Bulb Size
Ford OEM part. Single-filament wedge bulb (T20). Originally used in 2021+ Ford F-150, Bronco, and Maverick. 12V, 21W.	WT21W
ANSI standard (US & Canada). Dual-filament wedge bulb (T25). 12V, 27W/7W.	3157
ANSI standard (US & Canada). Single-filament wedge bulb (T20). 12V, 21W.	7440
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. 12V.	2356
ANSI standard (US & Canada). Festoon bulb, specialty application. 12V.	2456
ANSI standard (US & Canada). Single-filament wedge bulb (T25). 12V, 27W.	3156

Other Locations

Additional Notes

The Ford F-550 Super Duty back up light specifications span model years 1999 through 2022 and reference seven distinct bulb types across that period.
The 921 is the most frequently specified bulb across these years, covering the 2011-2016 model years as well as 2007, making it a T15 wedge bulb rated at 12V and 16W under the ANSI standard.
The WT21W covers the 2020-2022 Ford F-550 Super Duty and is a Ford OEM single-filament T20 wedge bulb rated at 12V and 21W, originally introduced on the 2021 Ford F-150, Bronco, and Maverick.
The 7440 is an ANSI-standard single-filament T20 wedge bulb rated at 12V and 21W, specified for the 2017-2018 model years. Although the WT21W shares the same T20 form factor and wattage rating, it is a Ford OEM part and the two are not confirmed as interchangeable.
The 3157, specified for the 2019 model year, is a dual-filament T25 wedge bulb rated at 12V with a 27W main filament and a 7W secondary filament. Its dual-filament design distinguishes it from the single-filament 3156, which was used in the 1999 and 2001 model years at 12V and 27W.
The 2356 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V, and is specified for the 2002, 2006, 2009, and 2010 model years. Its bayonet base makes it physically incompatible with the wedge-base bulbs used in other model years.
The 2456 is a festoon-style bulb rated at 12V and is noted as a specialty application type. It is specified for the 2000, 2003-2005, and 2008 model years.
The back up light bulb type for the Ford F-550 Super Duty changed multiple times across consecutive model years, indicating that direct substitution between adjacent years is not reliable without confirming the specific bulb type for each year.