Have the key on, the 4wd switch on, and the tranny in a forward gear.

To get to the hub mechanism, pop the cap off the end of the hub, remove the axle nut, and everything comes out that way. You will have to remove the brake caliper to get the hub off.
On re-assembly be sure the 3 tabs of the armature plate are in the 3 notches of the roller cage (it will explain itself when you see it). If not assembled aligned properly, the hub will not lock, and you will warp the plate.
Torque the nut to 100 inch pounds, spin the wheel around to set the bearings, and re-tighten to 100 inch pounds. If the cotter pin won't line up, tighten until it does.

Farmr

 

Thanks. So that flat washer with the 3 notches is the armature plate? (I had the guts out of the hub to clean). If the elect. is at the hub, and 4x4 is turned on, I should feel the armature plate "pull" magnetically like a solinoid ?

 

If the hub is apart, and power is to the magnet, the armature plate (the washer-looking thing with 3 tabs) should stick to the magnet.

To have power to the magnet you need

key on
4wd switch on
tranny in a fwd gear

The magnet doesn't actually move like a solenoid, it merely 'sticks' the plate to it. If the plate sticks, the mag is good.