Anti-Theft Horn
WARNING: This page is about a different car, the 2002 Lexus GS 430 and 2002 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.
Inspect the anti-theft horn operation. Connect the positive (+) lead from the battery to terminal No. 1 and the negative (-) lead to the anti-theft horn body, and check that the anti-theft horn blows. See CONNECTOR IDENTIFICATION . If operation is not as specified, replace the horn.