Plymouth Conquest front turn signal bulbs use 1156 size while rear turn signal bulbs use 1157 size. The replacement chart covers 1984 to 1986 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 Plymouth Conquest uses the 1156 bulb for the front turn signal across the 1984-1986 model years.
The 1156 is a single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, and recognized under the ANSI standard in the US and Canada.
The rear turn signal on the Plymouth Conquest uses the 1157 bulb across the same 1984-1986 model years.
The 1157 is a dual-filament bulb rated at 12V with a 21W/5W output, fitted with a BAY15d bayonet base, and also recognized under the ANSI standard in the US and Canada.
The BA15s base of the 1156 and the BAY15d base of the 1157 are not interchangeable. The BAY15d base features offset pins to prevent incorrect installation, while the BA15s base has a single contact and symmetrical pins.
The dual-filament design of the 1157 allows it to serve both a running light function at 5W and a turn signal function at 21W within a single bulb, which is why it is suited for rear applications where combined lighting functions are common.
Despite sharing the same 21W output at full brightness, the 1156 and 1157 are not interchangeable due to their differing base types and filament configurations.