It is the switch on the dash that totally locks up first the rear diff, then with a second click it will lock up the front diff. The Jeep will be very difficult to steer with both lockers on,
In order to activate the axle lock you must first shift into 4L (4wd low). Once in 4L, press the switch once to lock the rear axle, a second time to also lock the front. Pressing the switch a third...