Mercury Bobcat front turn signal bulbs utilize 1034NA or 1157NA size specifications, while rear turn signal bulbs require 1157 size. The replacement chart covers 1975 through 1980 model years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercury Bobcat front turn signal uses two distinct bulb types across its production years, with the 1034NA fitted in 1975 and 1979-1980, and the 1157NA fitted in 1976-1978.
The rear turn signal on the Mercury Bobcat uses the 1157 bulb uniformly across all listed model years, from 1975-1980.
All three bulb types present in these specifications, the 1034NA, 1157NA, and 1157, share the BAY15d bayonet base and a 12V, 21W/5W dual-filament configuration.
The BAY15d bayonet base is a double-contact offset-pin base, a design that physically prevents incorrect single-filament bulb installation in a dual-filament socket.
The 21W/5W rating on all three bulb types indicates a high-intensity filament for the active turn signal function and a lower-intensity filament for a secondary function such as parking or running light operation.
The 1034NA is described as a variant of the 1157, sharing its base type and voltage and wattage ratings, but distinguished by its natural amber glass envelope rather than a clear one.
The 1157NA similarly carries natural amber glass, which produces an amber output without relying on an amber lens, a relevant fitment detail when the housing uses a clear or non-tinted lens.
The 1157 used at the rear carries no amber designation, indicating a clear glass envelope, which means the amber color of the rear turn signal is produced by the lens rather than the bulb itself.
Because the 1034NA and 1157NA share the same base, voltage, and wattage as the 1157, physical installation is possible across types, but substituting a clear 1157 for an NA-designated bulb in a clear-lens housing would alter the output color.
All bulb types in these specifications conform to ANSI standards applicable in both the United States and Canada.