his truck is truck is TTB, with automatic locking front hubs, sounds like one of the hubs is bad, being that the front diff is open, if one hub is bad, there will be no power transmitted to the ground. is the front driveshaft turning when it is in 4x4? check that first.
also, rangers never had the actuator on the front axle, that is explorer stuff. SLA rangers either have pulse vacuum hubs or liveaxle, neither of which apply to the OP