The Bertone X-1/9 front and rear side marker bulbs both use a 158 size bulb specification. The replacement chart covers vehicle production spanning 1984 to 1989.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Bertone X-1/9 uses the 158 bulb in both the front and rear side marker positions across the 1984-1989 model years.
The 158 is a miniature wedge-type bulb, classified under the T10 form factor, which refers to a tubular glass envelope roughly 10 eighths of an inch wide.
The wedge base design means the bulb is held in place by the socket gripping the glass base directly, with no separate metal base or pins involved.
The 158 operates at 12 volts and draws 3 watts, placing it among the lower-wattage bulbs used in automotive marker lighting applications.
The 158 conforms to ANSI standards and is recognized for use in both the United States and Canada, indicating a standardized specification shared across North American markets.
Because the same bulb number applies to both the front and rear side marker positions on the Bertone X-1/9, a single bulb type serves all four side marker sockets on the vehicle.
T10 wedge bulbs are available from multiple manufacturers under various part numbers, though fitment depends on the bulb meeting the 12V, 3W electrical rating of the 158 specification.
The low wattage of the 158 bulb is consistent with its role as a marker light rather than a primary illumination source, as side markers are intended for vehicle visibility rather than road lighting.