Jeep J-3700 Back Up Light Bulb Size

The Jeep J-3700 back up light requires a P21W bulb size for proper installation and function. Data for 1156 replacements covers the period from 1965 through 1968.

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
1965-1968	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 is the sole bulb type listed for the backup light position across all model years covered in these specifications.
The 1156 is a single-filament bulb, meaning it serves one lighting function rather than sharing a housing with a dual-purpose filament for combined stop and tail duties.
It operates on a 12-volt electrical system and draws 21 watts, which is consistent with standard incandescent automotive backup lighting 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-pin BA15d base used on some other automotive bulbs.
The 1156 carries ANSI standardization recognized in both the United States and Canada, placing it within a regulated specification for base dimensions and electrical ratings.
The Jeep J-3700 used the 1156 bulb for backup lighting across the 1965-1968 model years, indicating a consistent electrical and fitment specification throughout that production span.
Because the BA15s base is a single-contact bayonet fitting, it is not interchangeable with dual-contact BA15d bulbs even though the physical housing size may appear similar.