Normal Operation
WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
When the key is inserted into the ignition cylinder, the key-in-ignition switch (part of the ignition switch) closes circuit 158 (BK/PK) to the smart junction box (SJB). The 12 volt input signals the SJB that the key is inserted. If the instrument cluster detects that the ignition switch is in the OFF or ACC position and the SJB communicates to the instrument cluster that the key is inserted in the ignition cylinder and the driver door is ajar, the key-in-ignition warning chime (located in the instrument cluster) sounds.