Safety Belt Warning Indicator
WARNING: This page is about a different car, the 2003 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.
The safety belt warning indicator illuminates when the driver safety belt is not fastened. The driver safety belt switch (part of the retractor) is hard-wired to the instrument cluster and provides the input into the instrument cluster signaling when the safety belt is connected. The instrument cluster then illuminates the bulb depending on the safety belt retractor position.