1998 Ford Expedition 4X4 wont engauge

When I first start the vehicle I can hear something under the dash clicking im guessing its the relays. And my 4x4 light is on but its not in 4x4 and I have the switch pointing to the 2wd and when I turn the switch nothing happens I had the switch tested and it came back fine. When I have the vehicle jacked up the front drive shaft turns with the wheels. Back to the transfer case switch on the dash if I take it completely apart and turn it with my hand I can get it to lock in 4lo. Thanx for the support