Chevrolet Repair: 98 CHEVY Z71 4X4, chevy z71, neutral safety switch

Question
MY FRIEND OWNS A 98 Z71 EXTRA CAB WITH ABOUT 120K. EVERYTHING WORKED WHEN HE BOUGHT THE TRUCK, BUT JUST A FEW WEEKS AGO THE 4X4 STARTED ACTING UP. IT HAS THE ELECTRONIC TRANSFER CASE, WHICH IS WORKING. THE DRIVESHAFT TO THE FRONT DIFFERENTIAL WILL TURN WHEN ENGAGED. HOWEVER, THE DIFFERENTIAL WILL NOT ENGAGE THE AXLES. HE HAS REPLACED THE ELECTRONIC ACTUATOR TO NO AVAIL. THERE HAVE BEEN NO NOISES OR PROBLEMS FROM THE FRONT END, JUST STOPPED WORKING. THE OBVIOUS THINGS HAVE BEEN CHECKED (WIRING, FUSES, ETC.) DOESN'T THE ACTUATOR MOVE WHAT IS BASICALLY A SHIFT FORK LIKE IN A MANUAL TRANS TO LOCK THE INPUT SHAFT(DRIVESHAFT) TO THE DRIVE AXLES? IF SO, THAT DOESN'T LEAVE MANY POSSIBILITIES FOR WHAT MIGHT BE WRONG. I MEAN EVERYTHING IS OBVIOUSLY OK IN THE SYSTEM UP TO THE DIFFERENTIAL (CONSIDERING PROPER VOLTAGES AND GROUND, WHICH I HAVE NOT CHECKED YET.) MAYBE YOU CAN HELP. THANKS A LOT.

Answer
Yes, the actuator shifts a collar in there, but it is on the right side axle shaft, which is disconnected from the differential when not engaged. The collar just locks it in.
One thing to check, along with the voltage, is the switch on the transfer case that senses when it is in four wheel drive, and sends power to the actuator. That switch looks like a little neutral safety switch, or an old style backup light switch, and a ball just drops into a groove on the shift rail, and closes the switch. Sends 12 volt battery voltage to the actuator.

Van