Yo,
Ok, I figured you tested the hubs, but needed to ask anyway.
Check the brown wire;
"The magnetic clutch is energized to hold the 4WD sprocket. The transfer case control module then rotates the internal cam with the electric motor to lock the 4WD sprocket. Once the transfer case is in 4HI, the magnetic clutch is released.
Clutch is 1.5 to 5.0 Ohms
Disconnect the Flat 8-pin square connector. Measure the magnetic clutch resistance between the harness side pin 5 and ground. It should be 1.5-5.0 ohms. With the transfer case in 2WD and the engine off, apply 12 volts to the harness side of pin 5 for a second. The clutch should click to lock the 4WD sprocket. At the 8-pin square connector, apply 12 volts to pin 4 and ground pin 6 for about one second. The electric motor should rotate clockwise stopping at the 4L position. Reverse the polarity and the electric motor should rotate counterclockwise stopping at the 2H position. Reconnect the 8-pin square connector. " by Ford