Mercury Montego front and rear turn signal bulbs utilize 3157NA, 1157NA, and 1034NA sizes, with the bulb specifications varying across model generations. The replacement chart covers 1968 through 2007 production years and documents corresponding turn signal bulb size requirements.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Mercury Montego turn signal specifications reference four bulb types across front and rear positions: 3157NA, 1157NA, 1034NA, and 1157.
The 3157NA is a dual-filament T25 wedge bulb rated at 12V with a 27W high filament and 7W low filament, constructed with natural amber glass and conforming to ANSI standards for the US and Canadian markets.
The 1157NA and 1157 are both dual-filament bulbs sharing the BAY15d bayonet base and a 12V, 21W/5W rating. The NA suffix denotes natural amber glass, while the 1157 without a suffix uses clear glass, relying on a colored lens for amber output.
The 1034NA is a variant of the 1157 series, sharing the BAY15d bayonet base and the same 12V, 21W/5W rating, with natural amber glass construction.
The BAY15d base found on the 1157, 1157NA, and 1034NA features two offset pins at different heights, a design that prevents incorrect single-filament substitution and ensures correct filament-to-circuit alignment.
The Mercury Montego (2005-2007) uses the 3157NA in both the front and rear turn signal positions, making it the sole bulb type for that generation across both applications.
For the 1968-1976 Montego, the front and rear turn signal positions do not consistently share the same bulb type. The rear position uses the 1157 across all those model years, while the front position alternates between 1157NA, 1034NA, and 1157 depending on the specific year.
The 1034NA and 1157NA are not interchangeable without consideration, despite sharing the BAY15d base and identical wattage ratings. The 1034NA is a recognized variant of the 1157 series, and fitment should follow the year-specific specification rather than assumed cross-compatibility.
The 1970 Montego front turn signal is specified with the 1157 rather than the 1157NA used in adjacent model years, indicating a clear glass bulb was factory-specified for that position in that year.
The 3157NA wedge base is physically distinct from the BAY15d bayonet base used by the 1157 series, meaning no direct substitution is possible between the bulb types used in the 1968-1976 and 2005-2007 generations.