Ford F-350 Super Duty Back Up Light Bulb Size

The Ford F-350 Super Duty back up light utilizes unique bulb sizes including WT21W, 7440, 3157, 921, 2356, 2456, 3156, and 2456. Available data covers a range from 1999 to 2023.

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
2023	WT21W
2021-2022	7440
2020	7440 (All Second Unit Body, Less Blind Spot Information System)
2019	3157
2017-2018	7440
2011-2016	921
2010	2356
2009	921
2006-2008	2356
2004-2005	2456
2002-2003	3156
2001	2456
2000	3156
1999	2456

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). Single-filament wedge bulb (T20). 12V, 21W.	7440
ANSI standard (US & Canada). Dual-filament wedge bulb (T25). 12V, 27W/7W.	3157
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 7440 bulb is the most frequently specified backup light size across the Ford F-350 Super Duty's model history, covering the 2017-2018, 2021-2022, and portions of the 2020 model year.
The 921 bulb, a T15 wedge type rated at 12V and 16W, is the second most recurring specification, appearing across the 2011-2016 model years as well as 2009.
The 7440 and WT21W are both T20 single-filament wedge bulbs rated at 12V and 21W, meaning they share the same wattage and base family, though the WT21W is a Ford OEM part rather than an ANSI-standardized unit.
The 2023 Ford F-350 Super Duty specifies the WT21W, which is a Ford OEM bulb originally introduced on the 2021 F-150, Bronco, and Maverick, making it a manufacturer-specific fitment rather than a universal ANSI replacement.
The 3157 bulb specified for the 2019 model year is a dual-filament T25 wedge type rated at 12V with a 27W high and 7W low filament, which differs structurally from the single-filament 7440 used in adjacent model years.
The 3156 and 7440 are both single-filament wedge bulbs rated at 27W and 12V, but the 3156 uses a T25 base while the 7440 uses a T20 base, making them physically non-interchangeable despite their matching wattage.
The 2356 bulb, specified for the 2006-2008 and 2010 model years, uses a BAY15d bayonet base rather than a wedge base, representing a fundamentally different mounting type from all other bulbs in these specifications.
The 2456 is classified as a festoon bulb for specialty applications, a form factor distinct from the wedge and bayonet types found elsewhere in these specifications, and it appears across the 1999, 2001, 2004-2005 model years.
The 2020 Ford F-350 Super Duty carries a conditional fitment note, specifying the 7440 only for vehicles designated as All Second Unit Body and Less Blind Spot Information System, indicating that trim or package configuration affects bulb selection for that year.
The 3156 single-filament T25 wedge and the 3157 dual-filament T25 wedge share the same physical base and housing size, but the 3157's second filament makes it electrically incompatible as a direct substitute in sockets wired for a single-filament application.