I have an F-150 with the 4WD shift switch on the dash. When I turn on the ignition I do not get the 4WD lights do not cycle, nor do i hear the shift relays click in the dash. Switching the dash switch will not switch it into 4WD. I have droped the the switching motor out and tested it and it runs fine. I have also removed the switching relay and jumpered the contacts for the switching motor and it will go into 4WD and light the dash light. The dash switch has 5 volts running to it. I'm stumped at this point. Could it be the GEM? ...Any help please....

 

It could be the GEM or even worse, electrical short. There is a TSB regarding this. For a shift on the fly to engage there are like 5 or so inputs it needs. Inputs from the brake switch, Neutral safety switch, speed sensor, ignition switch and one other I believe. They all send signals to the GEM which reads a signal from the switch which in turn sends a signal to the shift motor.

 

Check fuse #23 in the Central Junction Box. Inside cab left side of instrument panel.

JMC