Shift Solenoids SSA and SSB
WARNING: This page is about a different car, the 2004 Ford Pickup, 2004 Ford F550 Super Duty, 2004 Ford F450 Super Duty, 2004 Ford Excursion, and 2004 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
Shift solenoids SSA and SSB provide gear selection of first through fourth gears by controlling the pressure to the three shift valves.