Plymouth Belvedere Dome Light Bulb Size

The Plymouth Belvedere dome light utilizes bulb sizes 257 and 1004 for interior illumination across various production periods. Data provided for the specific lighting components covers the range from 1956 to 1971.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
1971	257
1956-1970	1004

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Festoon or BA9s base instrument bulb. 12V, 2W.	257
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. Variant of 1157. 12V, 21/5W.	1004

Other Locations

Additional Notes

The 1004 bulb is the dome light specification for the Plymouth Belvedere across the 1956-1970 model years.
The 1004 is an ANSI-standard bulb recognized in both the United States and Canada, rated at 12 volts with a dual-filament output of 21/5 watts.
Its BAY15d bayonet base uses two offset pins at different heights to ensure correct polarity orientation during installation, a design that prevents the filaments from being connected to the wrong circuit.
The 1004 is classified as a variant of the 1157, meaning the two types share a similar construction but are not necessarily interchangeable due to differences in filament wattage ratings between variants.
The 1971 Plymouth Belvedere dome light specification shifts to the 257 bulb, which differs substantially from the 1004 used in prior model years.
The 257 is a single-filament bulb rated at 12 volts and 2 watts, making it a considerably lower-output lamp than the dual-filament 1004.
The 257 is compatible with either a festoon or BA9s base fitting, indicating that the 1971 Belvedere dome light housing accepts one of those two socket types rather than the BAY15d bayonet used by the 1004.
Because the 1004 and 257 differ in base type, wattage, and filament count, the two bulbs are not interchangeable between the 1971 model year and earlier Belvedere applications.