4x4 not working

My moms 98 expedition eddie bauer when u turn on 4x4 switch the light kicks on and you hear the click. When she does this no front end action but sometimes if u turn in circles and go forward and backwards you will get it working. You never know if it will go. Where should i start without buying new parts first..THANKS DAVE

That is normal. Try just switching it into 4L while in neutral then put it in reverse and back up about 2-3 inches itll kick in .

I have a supercrew pickup basically the same thing i turn my switch at any time it goes right in. Sometimes it will not go in all day of trying anyone got any ideas?