Bertone X-1/9 Back Up Light Bulb Size

The Bertone X-1/9 back up light utilizes 1073 and P21W bulb sizes according to the provided specifications. Data for the bulb sizes covers the range from 1984 to 1989.

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
1989	P21W
1988	1073
1986-1987	P21W
1985	1073
1984	P21W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. Lower wattage variant of 1156. 12V, 13W.	1073

Other Locations

Additional Notes

The Bertone X-1/9 back up light specifications cover model years 1984-1989 and reference two distinct bulb types: the P21W and the 1073.
The P21W is an ECE-standard bulb used in European and worldwide automotive applications, operating at 12V with a 21W output and a BA15s single-contact bayonet base.
The 1073 follows the ANSI standard common to the US and Canadian markets, also operating at 12V but at a lower 13W output, and shares the BA15s bayonet base format.
Both bulb types are single-filament designs, which is consistent with their use in a back up light application where only one steady illumination state is required.
Although the P21W and 1073 share the same BA15s bayonet base, their wattage ratings differ by 8W, meaning they are not electrically equivalent and are not interchangeable without consideration of that difference.
The 1073 is described as a lower wattage variant of the 1156, a widely available ANSI bulb, which places it within a well-established North American bulb family while producing less light output than its 1156 counterpart.
The Bertone X-1/9 (1984) uses the P21W, while 1985 shifts to the 1073, indicating that the specified bulb type is year-specific and cannot be assumed consistent across the production run.
The years 1986, 1987, and 1989 all specify the P21W, while 1985 and 1988 specify the 1073, reflecting an alternating pattern across the listed model years rather than a single standardized fitment.