The Ford F-550 Super Duty front side marker uses a 12961 or 194 bulb size, while the rear side marker requires a 3157 or 12961 bulb size. The replacement chart covers vehicle production years spanning 1999 to 2022.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Ford F-550 Super Duty front side marker position uses two distinct bulb sizes across its model year range. The 194 bulb was specified for 1999-2010, while the 12961 bulb replaced it from 2011 onward through 2022.
The 12961 is a Philips part number for a miniature wedge bulb in the T10 form factor, rated at 12V and 5W with a W2.1x9.5d base. The 194 is an ANSI-standard T10 wedge bulb rated at 12V and 3.78W. Both share the T10 form factor, though their wattage and base designations differ.
Because the 12961 and 194 are both T10 wedge bulbs, physical fitment in the socket may be possible across both types, but the wattage difference of approximately 1.22W means they are not electrically identical replacements for one another.
The rear side marker position on the Ford F-550 Super Duty uses the 3157 bulb for 2011-2022 model years. For 2007-2010, the rear side marker instead used the 12961 bulb.
The 3157 is an ANSI-standard dual-filament wedge bulb in the T25 form factor, rated at 12V with a 27W high filament and a 7W low filament. Its dual-filament design and T25 body make it physically and electrically incompatible with the T10-based 12961 or 194 bulbs used elsewhere in the same vehicle.
A headlamp technology condition applies to the 2017-2019 Ford F-550 Super Duty. Both the front and rear side marker specifications for those years carry a "With Halogen Capsule Headlamps" qualifier, indicating the listed bulb sizes correspond specifically to that headlamp configuration.
The front and rear side marker positions do not share the same bulb type in any single model year. The two positions use different bulbs throughout the entire specification range, which means cross-position substitution is not supported by these specifications.
The W2.1x9.5d base designation on the 12961 bulb refers to a wedge-style base with a 2.1mm wire contact width and a 9.5mm pin spacing. This base type is standard across many T10 miniature wedge applications, though the Philips 12961 part number identifies a specific product within that category.
The 3157 bulb's dual-filament construction means it carries two independent circuits within one envelope. In side marker applications, typically only one filament is active, but the socket must be wired to accommodate the dual-filament base to function correctly.
Across the full specification range for the Ford F-550 Super Duty, three distinct bulb sizes are represented in the side marker positions: the 194, the 12961, and the 3157. Each occupies a different electrical and physical category, and none of the three is a direct substitute for either of the others.