Jeep J20 Back Up Light Bulb Size

The Jeep J20 back up light utilizes 1156 and P21W bulb sizes for the rear illumination system. Data for the specified vehicle covers the range from 1974 through 1988.

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
1974-1988	1156

Bulb Specifications

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

Other Locations

Additional Notes

The Jeep J20 uses the 1156 bulb for the back up light across all listed model years from 1974-1988.
The 1156 is an ANSI-standardized bulb type, meaning its specifications are governed by a recognized North American standard applicable in both the US and Canada.
The 1156 operates on a 12-volt electrical system and draws 21 watts, which is consistent with standard automotive incandescent backup lighting of that era.
The 1156 is a single-filament bulb, meaning it serves one lighting function only, as opposed to dual-filament types that handle two functions such as braking and running light simultaneously.
The 1156 uses a BA15s bayonet base, where "BA15s" denotes a bayonet fitting with a 15mm base width and a single contact pin, which determines physical socket compatibility.
The BA15s base type is not interchangeable with BA15d sockets, which use two offset pins rather than one, so substitutions between these base types are not physically compatible even when other electrical ratings match.
The single-filament 1156 is sometimes confused with the 1157, which shares a similar appearance but uses a BA15d dual-contact base and carries two filaments, making the two types mutually incompatible in the same socket.