Chevrolet Corvair Courtesy Bulb Size

The Chevrolet Corvair courtesy light uses bulb size 631 or 89 depending on the specific application for the interior lighting system. Data for the bulb sizes covers the range from 1960 to 1969.

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
1965-1969	631
1960-1964	89

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Variant of 1156. 12V, 21W.	631
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Lower wattage variant of 1156. 12V, 13W.	89

Other Locations

Additional Notes

The Chevrolet Corvair courtesy bulb specification splits across two distinct bulb types over its production run, with the 89 bulb used in 1960-1964 models and the 631 bulb used in 1965-1969 models.
Both the 631 and 89 are ANSI-standardized bulbs recognized in the United States and Canada, and both share the BA15s single-contact bayonet base configuration.
The BA15s base is a single-contact bayonet fitting, meaning the two types are physically interchangeable at the socket level, though their wattage ratings differ.
The 631 operates at 12 volts and 21 watts, while the 89 operates at 12 volts and 13 watts, representing a meaningful difference in power draw between the two fitment periods.
Both bulbs are described as single-filament types, which is consistent with a courtesy light application where simple on/off operation is required rather than dual-intensity switching.
Both the 631 and 89 are classified as variants of the 1156 bulb family, sharing its BA15s base but differing in wattage output from the standard 1156 rating of 26.9 watts.
Despite the shared base type between the 631 and 89, substituting one for the other in the Corvair courtesy light circuit would result in a mismatch with the original wattage specification for that model year.