How did you determine that your front axle is engaged?
Normally you neet to cut all 6 off the ground.
If you did that, please teach me too.
As far as the engagement switch at dash there also is an air switch at the transfer case which is a large washer connected to the Low Range arm below the cab, that switch might be stuck, if no problem there than you have to check the air cylinders on the transfer case.
PS also people here likes you to use your first post to be introducing your self before jumping into all the other fun problems...
You will probably find you'll get better results on forums if you post in the correct place. There is a forum for 5 tons. This forum is for "Forum Tips and Tricks". Not many people pay attention to what's here.