Seat Belt Buckle Switch
WARNING: This page is about a different car, the 2002 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect seat belt buckle switch 2-pin connector. See Fig 1. Check for continuity between seat belt buckle switch terminals. With seat belt buckle switch on (belt fastened), continuity should exist. With seat belt buckle switch off (belt unfastened), no continuity should exist. If continuity is not as specified, replace seat belt.