WARNING: This page is about a different car, the 2007 Ford Pickup, 2007 Ford F550 Super Duty, 2007 Ford F450 Super Duty, and 2007 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
Remove the safety belt buckle switch electrical connector from the seat cushion pan.
Fig 1: Locating Safety Belt Buckle Switch Electrical Connector