Chevrolet Bel Air Trunk Bulb Size

The Chevrolet Bel Air trunk light uses 1003, 89, and 94 bulb sizes according to the provided data. Information for the specified vehicle covers the range from 1955 to 1975.

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
1973-1975	1003
1972	89
1958-1971	1003
1955-1957	94

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1003
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Lower wattage variant of 1156. 12V, 13W.	89
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. Variant of 1157. 12V, 21/5W.	94

Other Locations

Additional Notes

The 1003 bulb is the dominant trunk bulb type across the Chevrolet Bel Air lineup, appearing in model years 1958-1975 with the sole exception of 1972, which uses the 89 bulb instead.
The 1003 is an ANSI-standard single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base, a single-contact base design that locates and locks the bulb with a twist.
The 89 bulb used in the 1972 Bel Air is also a single-filament BA15s type but operates at a lower 13W output, making it a lower-wattage variant of the 1156 bulb family rather than a direct equivalent of the 1003.
Although the 1003 and 89 share the same BA15s bayonet base, their wattage ratings differ, and substituting one for the other may affect socket load and light output in the trunk compartment.
The 1955-1957 Bel Air trunk uses the 94 bulb, which is physically and electrically distinct from the 1003. The 94 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V and 21/5W.
The BAY15d base on the 94 bulb has two offset pins rather than the single-contact BA15s base found on the 1003 and 89, meaning these bulb types are not physically interchangeable despite their similar appearance.
The 94 bulb is a variant of the 1157 family. Its dual-filament design, while common in stop and tail light applications, serves the trunk lighting function specifically on the 1955-1957 Bel Air.
All three bulb types listed, the 1003, 89, and 94, conform to ANSI standards applicable in the United States and Canada, indicating standardized ratings and base configurations across the range.