The Ferrari 328 GTB uses a 158 bulb size for both front and rear side marker applications. The replacement chart covers 1986 to 1989 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Ferrari 328 GTB uses the 158 bulb for both front and rear side markers across all listed model years, 1986-1989.
The 158 is classified as a miniature wedge bulb, corresponding to the T10 form factor, which describes a tubular glass envelope roughly 10mm wide at its widest point.
The 158 operates at 12 volts and draws 3 watts, placing it among the lower-wattage bulbs in automotive applications.
The wedge base design of the 158 means the bulb is retained by the socket through friction on the glass base itself, with no separate metal bayonet or screw fitting involved.
The 158 carries ANSI standardization recognized in both the United States and Canada, meaning its electrical and physical specifications conform to a defined North American standard.
The uniform use of the 158 across both front and rear positions means a single bulb type serves all four side marker locations on the vehicle.
T10 wedge bulbs are a widely produced form factor, and the 158 designation specifies a particular wattage and voltage rating within that broader family, so not all T10 wedge bulbs are interchangeable with the 158.