Ford Flex front turn signal bulbs utilize 3457NA and 3357NA sizes, while rear turn signal bulbs use 3157 and 4157 sizes. The replacement chart covers 2009 through 2019 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Ford Flex front turn signal uses the 3457NA bulb for the 2015-2019 model years, with the same fitment also applying to 2010, 2012, and 2013.
The 3457NA is a dual-filament T25 wedge bulb rated at 12V with a 27W/7W filament configuration, and its natural amber glass produces the legally required amber turn signal color without the need for an amber lens.
Three model years of the Ford Flex front turn signal, specifically 2009, 2011, and 2014, use the 3357NA instead of the 3457NA.
The 3357NA is a single-filament T25 wedge bulb rated at 12V and 27W, also featuring natural amber glass. Its single-filament design distinguishes it functionally from the dual-filament 3457NA despite sharing the same T25 form factor.
Because the 3357NA and 3457NA share the T25 wedge base, they are physically interchangeable in the socket, but substituting one for the other is not appropriate given the difference in filament count and intended circuit function.
The rear turn signal on the Ford Flex uses the 4157 bulb across the 2009-2018 model years, all noted as applying to vehicles with halogen capsule headlamps.
The 2019 Ford Flex rear turn signal departs from the 4157 specification used in prior years, instead calling for the 3157, also noted for halogen capsule headlamp fitment.
Both the 3157 and 4157 are dual-filament T25 wedge bulbs rated at 12V with a 27W/7W output, making their electrical characteristics identical, though they are distinct part numbers and are not confirmed as interchangeable by the specifications.
The "NA" suffix on the 3457NA and 3357NA designates natural amber glass, a coating or tinting applied directly to the bulb envelope, which is absent on the clear-glass 3157 and 4157 rear turn signal bulbs.
All four bulb types listed across both front and rear positions conform to ANSI standards applicable in the United States and Canada.