Jeff has you on the correct trail...but...in spite of the AWD switch showing that it is "ON" I would first verify that you are actually delivering 12V to the connection Jeff's diagram illustrates by using a multimeter on the pins on the proximal side of the connector. If you do have 12Volts then clean the connector well, re-connect, and check the front drive again. If still no front drive then proceed to test the coil. If it test good, as Jeff said, your armature plate is likely warped. A caveat- I have seen several members post that although the coil tested good (and the armature plate was not warped) it still did not induce enough magnetic field to put enough drag on the armature plate to allow the sprag to engage. In those cases the coil and armature plate were replaced and the problem corrected.
Pull out the diff. and unbolt the side cover. It contains the coil. Pull out the armature plate and lay on perfectly flat surface....if it warped, replace. If it has an uneven wear pattern, replace. You can also reconnect the coil to the harness, lay the armature plate flat against the coil and turn on AWD switch to energize the coil. You should have a difficult time sliding the arm plate off the magnetized coil. If it slides off with ease then the coil is likely bad. Also pull out the sprag cage and inspect it for cracks/damage while you are in there. I understand that you just had it rebuilt and hopefully the plastic cage was replaced with a billet upgrade...if not...get a billet one and replace it even if the plastic one looks OK.