Four-Wheel Drive (4WD) Low Switch
WARNING: This page is about a different car, the 2012 Ford F550 Super Duty and 2012 Ford F450 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
The 4WD Low switch sends a ground signal to the IC when the vehicle is in 4WD Low. The PCM then receives a 4WD Low status from the IC and adjusts the transmission shift schedule accordingly.