Chevrolet Townsman Back Up Light Bulb Size

The Chevrolet Townsman back up light uses 1156 and P21W bulb sizes for the rear illumination system. Data for the specific lighting components covers the period from 1969 to 1972.

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
1969-1972	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

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Additional Notes

The 1156 bulb is the sole back up light bulb size listed for the Chevrolet Townsman across the 1969-1972 model years.
The 1156 is an ANSI-standardized bulb type, meaning its physical and electrical specifications follow a defined North American standard recognized in both the United States and Canada.
The 1156 operates on a 12-volt electrical system and draws 21 watts, which is consistent with standard automotive reverse lighting applications of that era.
The 1156 uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin, distinguishing it from the dual-contact BA15d variant with which it is not interchangeable.
As a single-filament bulb, the 1156 serves one dedicated function per socket, unlike dual-filament types that handle two lighting functions from a single housing.
The BA15s base requires a quarter-turn locking motion for installation, a common fitment method in automotive sockets of that period.
Because the BA15s and BA15d bases share the same 15mm collar width but differ in pin configuration, substituting a dual-contact bulb in a single-contact socket is not mechanically compatible.