The Geo Tracker brake component requires a 1157 bulb size for proper installation and function within the lighting system. Data for the specified vehicle covers the range from 1989 to 1997.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Geo Tracker uses the 1157 bulb for brake lighting across all nine model years covered in the specifications, spanning 1989-1997.
The 1157 is a dual-filament bulb, meaning it serves two distinct lighting functions within a single unit. In brake light applications, the higher 21W filament activates for the stop signal, while the 5W filament handles a secondary function such as a tail or parking light.
The 1157 operates on a 12V system and uses a BAY15d bayonet base, a two-pin offset base design that prevents incorrect insertion by positioning the two pins at different heights along the base.
The center high mount stop light (CHMSL) on the Geo Tracker uses the 921 bulb for model years 1992-1997.
The 921 is a single-filament wedge bulb in the T15 form factor, rated at 12V and 16W. Unlike the 1157, it has no secondary filament and is dedicated solely to the stop light function in the CHMSL position.
The 921 wedge bulb uses no base pins, relying instead on tension from the socket contacts along the sides of its plastic wedge base to maintain the electrical connection.
The 1157 and 921 are not interchangeable. Their base types, filament counts, and wattage ratings are distinct, and each is assigned to a specific lighting position on the vehicle.
Both the 1157 and 921 are ANSI-standardized bulbs recognized in the United States and Canada, meaning their electrical and physical specifications conform to a defined industry standard rather than a proprietary format.