The Saturn Relay brake light utilizes bulb size 3157 and bulb size 2458 for the specified lighting components. Data for the lighting specifications covers the range from 2005 to 2007.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Saturn Relay uses two distinct bulb types across its brake lighting system for the 2005-2007 model years: the 3157 for standard brake lights and the 921 for the center high mount stop light.
The 3157 is a dual-filament wedge bulb operating at 12V with a wattage split of 27W and 7W, conforming to ANSI standards recognized in both the United States and Canada.
The dual-filament design of the 3157 allows a single bulb to serve two functions within the same housing, with the higher 27W filament typically dedicated to braking and the lower 7W filament to running or parking light operation.
The 921 is a single-filament wedge bulb rated at 12V and 16W, also conforming to ANSI standards for the US and Canadian markets.
The T25 designation of the 3157 and the T15 designation of the 921 refer to their respective wedge base sizes, with T25 being physically larger than T15.
Because the 3157 and 921 use different base sizes, the two bulb types are not interchangeable within the Saturn Relay's brake lighting system.
The center high mount stop light on the Saturn Relay (2005-2007) uses the 921, a single-filament bulb, which is consistent with that position serving only one lighting function.
Both the 3157 and 921 share the same 12V operating voltage, aligning with the standard 12-volt electrical systems found in passenger vehicles of this type.