The Ford Mustang II front turn signal requires a 1157 or 1034NA bulb size, while the rear turn signal uses a 1156 or 1157 bulb size. The replacement chart covers 1974 through 1978 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 Mustang II uses three distinct bulb types across its front and rear turn signal positions: the 1157, 1034NA, and 1156, all of which conform to ANSI standards recognized in the United States and Canada.
The 1157 is a dual-filament bulb rated at 12V with a 21W main filament and a 5W secondary filament, mounted on a BAY15d bayonet base. The dual-filament design allows a single bulb to serve both turn signal and parking light functions simultaneously.
The 1034NA shares the same BAY15d bayonet base and 12V, 21W/5W electrical ratings as the 1157 but is distinguished by its natural amber glass envelope, which produces a colored output without relying on a separate amber lens.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base. Because it carries only one filament, it serves a dedicated signaling function rather than a combined signal-and-parking role.
The BAY15d base used by the 1157 and 1034NA differs from the BA15s base used by the 1156. These two base types are not interchangeable, as the BAY15d features offset pins to align the dual-filament contacts correctly, while the BA15s uses a single-contact design.
The Ford Mustang II front turn signal position used the 1157 for the 1976-1978 model years and the 1034NA for the 1974-1975 model years. Both are dual-filament bulbs on BAY15d bases, making them electrically similar despite the glass color difference.
The rear turn signal position used the 1157 exclusively in the 1975 model year, while the 1156 was specified for 1974 and 1976-1978. The 1975 rear application of the 1157 represents the only year in which a dual-filament bulb was used at that position.
Because the 1975 rear turn signal calls for the 1157 (BAY15d base) while surrounding model years call for the 1156 (BA15s base), substituting a 1156 into a 1975 rear socket would result in a base mismatch and an incorrect fitment.
The 1034NA, used at the front position in 1974-1975, is a variant of the 1157. Despite their functional similarity, the amber glass of the 1034NA means it is not a visually identical replacement in applications where a clear-glass bulb behind an amber lens is expected.