Mercury Zephyr front and rear turn signal bulbs utilize 1157 and 1157NA sizes, with front applications accepting either bulb size and rear applications requiring the 1157 bulb. The replacement chart covers 1978 to 1983 model 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 1157 bulb is the dominant type across both front and rear turn signal positions in the Mercury Zephyr, appearing in all six model years covered by the rear turn signal data and in four of the six front turn signal years.
The 1157 is a dual-filament bulb rated at 12 volts with a 21W/5W power draw, meaning the higher wattage filament handles the turn signal function while the lower wattage filament serves a secondary role such as parking or running light duty.
Both the 1157 and 1157NA share the BAY15d bayonet base, a two-pin offset base design that physically locks the bulb into the socket at a fixed rotational position to align the filaments correctly.
The 1157 and 1157NA are both classified under ANSI standards applicable in the United States and Canada, indicating standardized electrical and physical specifications across manufacturers.
The 1157NA differs from the standard 1157 solely in its natural amber glass envelope, which produces an amber-colored output without the use of an amber-tinted lens on the vehicle.
The Mercury Zephyr front turn signal positions for 1978-1979 specify the 1157NA rather than the clear 1157, indicating those model years relied on the bulb itself to produce the amber signal color at the front.
Because the 1157 and 1157NA share identical base types and electrical ratings, the physical fitment is interchangeable between the two; however, substituting a clear 1157 for an 1157NA in a clear-lens housing would alter the output color from amber to white.
The rear turn signal position uses the standard 1157 across all model years from 1978-1983, suggesting the rear housings on the Zephyr incorporated amber or red lenses to achieve the required signal color independent of the bulb glass.