Chevrolet Chevette Courtesy Bulb Size

The Chevrolet Chevette courtesy light utilizes bulb sizes 631, 561, and 89 depending on the specific version of the vehicle. Available data covers the range from 1976 to 1987.

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
1979-1987	631
1977-1978	561
1976	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). Festoon bulb, 44mm length, end-cap contacts. 12V, 12W.	561
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 Chevette courtesy bulb specification changed across its production run, with three distinct bulb types used: the 631, the 561, and the 89.
The 631 bulb was specified for the Chevrolet Chevette across the longest portion of its production span, covering model years 1979-1987.
The 631 is a single-filament bulb with a BA15s bayonet base, rated at 12V and 21W, and is classified as a variant of the more widely known 1156 bulb type.
The BA15s bayonet base uses a single contact pin, which is a defining fitment characteristic that distinguishes it from dual-pin bayonet bases used in other bulb families.
Model years 1977-1978 used the 561, a festoon-type bulb with a 44mm length and end-cap contacts, rated at 12V and 12W.
The festoon format of the 561 is physically and electrically incompatible with the BA15s bayonet socket used by the 631, meaning the two bulb types are not interchangeable despite both operating at 12V.
The 1976 model year used the 89 bulb, also a single-filament BA15s bayonet type, rated at 12V and 13W.
Although the 89 and 631 share the same BA15s bayonet base, their wattage ratings differ significantly, at 13W and 21W respectively, which affects light output and socket load.
All three bulb types conform to ANSI standards applicable in both the United States and Canada.
The shift from the 89 in 1976 to the 561 in 1977, and then to the 631 in 1979, reflects two separate socket format changes within the Chevette courtesy light system across those model years.