Chevrolet Repair: Auto locking hubs, auto locking hubs, transfercase

Question
Hi Wayne. I have a 1997 K3500 with manual engaging 4WD. I engaged the 4WD today and the front hubs absolutely would not lock in. The transfer case is engaging. All that the manual tells me is that the hubs are automatic. I was wondering if they are elec., vacuum, or air activated and if this could be the problem. I will greatly appreciate any advise or input that you could give me to resolve this problem.

Answer
Hey,

 The actuator on the front diff is probably defective.  There is a little module bolted to the passengers side of the diff and has two wires that go to it.  You should have 12v and ground at those wires when  the transfercase is applied.  It unlocks and locks the front diff.

Wayne