im just learning on my 3rd gen stuff.on my 2nd gen i installed a vacuum switch on the line going to the front dif so i could use 4 lo without the hubs engagaed,do the 3rd gens use vacuum to engagae the front end?it doesnt look the same as my 2nd gen.thanx

 

3rd gens have locked hubs on the front, the tcase does everything. meaning the front driveline is spinning anytime the truck is moving.
the only way to unlock them is to put on one of the dynatrac kits.