The Isuzu I-Mark uses 194 and 89 bulb sizes for front side marker applications, with 194 bulb size designated for rear side marker positions. The replacement chart covers vehicle production spanning 1981 to 1989.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Isuzu I-Mark uses two distinct bulb types across its side marker positions: the 194 and the 89, both of which conform to ANSI standards recognized in the United States and Canada.
The 194 is a miniature wedge bulb in the T10 form factor, rated at 12V and 3.78W. Its wedge base design means it is retained by friction rather than a locking mechanism, requiring no rotation during installation or removal.
The 89 is a single-filament bulb with a BA15s bayonet base, rated at 12V and 13W. The BA15s base uses a single contact pin and requires a quarter-turn to lock into its socket, a fitment method that is mechanically incompatible with wedge-style sockets.
At 13W, the 89 draws considerably more power than the 3.78W 194, meaning the two bulb types are not electrically or physically interchangeable despite both operating on a 12V system.
The 89 is described as a lower wattage variant of the 1156. While the two share the BA15s bayonet base, the wattage difference means the 1156 is not a direct substitute for the 89 in these marker positions.
On the Isuzu I-Mark, the front side marker used the 89 bulb from 1981-1986, then transitioned to the 194 for 1987-1989, indicating a socket type change at the front position between those model years.
The rear side marker on the Isuzu I-Mark used the 194 bulb across all listed years from 1981-1989, making it consistent throughout the entire production span covered by these specifications.
Because the front marker socket changed between the 1986 and 1987 model years, a 194 wedge bulb sourced for a 1987-1989 front position is not compatible with a 1981-1986 front socket, which requires the BA15s-based 89.
From 1987-1989, both the front and rear side marker positions on the I-Mark use the same 194 bulb, meaning a single bulb type services all four side marker positions on those model years.