4x4 Low Switch
WARNING: This page is about a different car, the 2005 Ford Pickup, 2005 Ford F550 Super Duty, 2005 Ford F450 Super Duty, and 2005 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
The 4x4 low switch sends a ground signal to the instrument cluster when the vehicle is in 4x4L. The PCM then receives 4x4L status from the instrument cluster and adjusts the transmission shift schedule accordingly.