Four-Wheel Drive (4WD) Low Switch
WARNING: This page is about a different car, the 2008 Ford Pickup, 2008 Ford F550 Super Duty, 2008 Ford F450 Super Duty, and 2008 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
The Four-Wheel Drive (4WD) Low switch sends a ground signal to the Instrument Cluster (IC) when the vehicle is in 4WD Low. The PCM then receives 4WD Low status from the IC and adjusts the transmission shift schedule accordingly.