Did you ever figure this out? I've swapped my instrument cluster out for one from a 2001 F-350 with a tach. It has input for the 4x4 and low indicators. I have nothing attached to the connection on the transfer case at the moment.
I think I've discovered the sensor is a 4L3Z-7E440-AB and the connector is a Motorcraft WPT1081. I have not ordered one yet.
Anywhere I can find the connector is outrageously expensive.