White/GMC ACM front side marker bulbs use 1157 size while rear side marker bulbs use 194 size. The replacement chart covers 1988 to 1992 production years with bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The White/GMC ACM uses the 1157 bulb for the front side marker position across the 1988-1992 model years.
The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12V with a 21W/5W output, conforming to ANSI standards for the US and Canada.
The dual-filament design of the 1157 means it carries two separate tungsten filaments within a single envelope, each operating at a different wattage.
The BAY15d bayonet base features two offset pins, which physically prevents single-filament bayonet bulbs from being seated in its place.
The rear side marker position on the White/GMC ACM uses the 194 bulb across the same 1988-1992 model years.
The 194 is a miniature wedge bulb in the T10 form factor, rated at 12V and 3.78W, also conforming to ANSI standards for the US and Canada.
The T10 wedge base relies on the tension of its wire leads rather than a locking mechanism, making it incompatible with bayonet-style sockets.
The 1157 and 194 serve distinct socket types, and the two bulbs are not interchangeable with each other despite both operating on a 12V system.
The wattage difference between the 1157 and the 194 reflects their respective roles, with the higher-output 1157 at the front and the lower-output 194 at the rear.
Both the 1157 and 194 are governed by ANSI standards, meaning physically and electrically equivalent substitutes from different manufacturers are expected to conform to the same specifications.