Anti-Theft Horn
WARNING: This page is about a different car, the 2003 Lexus RX 300 and 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.
Connect the positive (+) lead from the battery to terminal 1 and negative (-) lead to the anti-theft horn body, and check that the anti-theft horn blows. See Fig 1. If operation is not as specified, replace the horn.