The Dodge D400 front turn signal uses a 1157 or 1157NA bulb size, while the rear turn signal requires either a 1157 or 198 bulb size. The replacement chart covers 1978 through 1981 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 1157 is the most frequently specified bulb across the Dodge D400 turn signal positions, appearing in both the front and rear turn signal roles for the 1979-1981 model years.
The 1157 is a dual-filament bulb rated at 12V with a 21W high filament and a 5W low filament, mounted on a BAY15d bayonet base, which allows it to serve both turn signal and parking light functions from a single socket.
The BAY15d bayonet base uses two offset pins to ensure correct orientation during installation, preventing the filaments from being wired to the wrong circuit.
The 1157NA specified for the 1978 Dodge D400 front turn signal shares the same BAY15d base and 12V, 21W/5W electrical ratings as the standard 1157, but its glass envelope is tinted natural amber rather than clear.
Because the 1157NA produces an amber output through its tinted glass, it is not a direct cosmetic substitute for the clear 1157 in housings that rely on a colored lens to produce the amber signal color.
The 198 bulb specified for the 1978 Dodge D400 rear turn signal is a miniature wedge type in a T5 form factor, rated at 12V and 2W, which represents a substantially lower wattage than the 1157 used in the same position on later model years.
The 198 uses a wedge base rather than a bayonet base, making it physically incompatible with sockets designed for the BAY15d mount used by the 1157 and 1157NA.
The 198 is also a single-filament bulb, unlike the dual-filament 1157, meaning the two bulb types serve different circuit configurations and are not interchangeable regardless of socket compatibility.
All three bulb types listed, the 1157, 1157NA, and 198, conform to ANSI standards recognized in both the United States and Canada.