Ford LTD II front side marker bulbs use 194NA or 194 size, while rear side marker bulbs use 1157 size. The replacement chart covers 1977 to 1979 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 LTD II rear side marker position uses the 1157 bulb across all three model years covered, spanning 1977-1979.
The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 21W/5W output, meaning it carries separate wattage ratings for its two filaments.
The BAY15d bayonet base features offset pins, which physically prevents incorrect single-filament bulbs from being seated in the same socket.
The front side marker position on the 1977-1978 LTD II uses the 194, a miniature wedge T10 bulb rated at 12V and 3.78W.
For the 1979 model year, the Ford LTD II front side marker specification changes to the 194NA, which shares the same T10 wedge form and 12V, 3.78W electrical rating as the 194 but incorporates natural amber glass.
Because the 194NA produces its amber color through tinted glass rather than a colored lens or housing, substituting a clear 194 in the 1979 front position would alter the emitted light color.
Both the 194 and 194NA conform to ANSI standards recognized in the US and Canada, placing them within the same standardized miniature bulb classification system.
The T10 wedge base used by both the 194 and 194NA relies on the bulb's glass envelope and wire leads for retention rather than a separate metal base, which is a defining characteristic of the wedge base design.
The significant wattage difference between the front marker bulbs (3.78W) and the rear 1157 (up to 21W on its primary filament) reflects the dual functional role the rear position serves, combining both marker and stop or tail light duties within a single bulb.