Hello I saw your post and just have a few questions. I am new to this forum and I have a 1997 F-150 XLT 4.6 Liter with "W" code engine with shift on the fly shift **** control. My 4x4 hasn't worked for a while and I have been throwing parts it it and still don't work. The symptoms I have is that the 4x4 high and low lights come on when I turn the key to start the truck in the instrument panel. But when I turn the switch to any position to engage the 4x4 nothing happens. I have installed a new transfer case shifter motor, new vacuum actuators on the firewall Both have been replaced. new vacuum actuator on the front transfer case, I been looking for a transfer case shift relay but cant find one. My part number is F75B-14B194-BC I can find this part number but ending in AC,CA,BB and mine ends in BC does this part have to be exactly ending in BC and can you please tell what these abbreviations means for my educations purpose. I will try to test my module according to your instructions with a 12 volt battery. I figured that this transfer case relay is bad due to the fact I am not getting any power to the transfer case motor in any of the positions I select for the selector switch. In closing, I will try to see on this forum how to test for a GEM module. thanks

 

Crash, you waisted a lot of money and time replacing parts just hoping the get the system fixed.
Reading you description tells me the GEM is faulty.
You cannot test it by simple methods because it is a digital module (General Electronic Module) that does many different functions on your vehicle not just 4x4..
The dash 4h and 4l lamps are turned on by the GEM but not until the system runs the case motor to either position. If the lights 'stay on' after Dash check-out has completed, the GEM is faulty.

Of course the case motor will not receive power if the GEM does not operate the case motor relay [assuming the fuse is not blown] for power to that relay.
The case motor, front Actuator and firewall solenoids are only directed by the GEM to operate and are not the trouble you describe.
The replacement GEM has to be the correct one for the build options the truck has.
Look for a water leak finding it's way to the GEM.
Pays to know how a system works before trying to work finding a fault.
Good luck.

 

Thanks appreciate the quick reply I’ll try to look at GEM module for the truck.

 

I recently started having this issue as well. As far as I can tell there's no water anywhere (recently had the windshield replaced), unless it's dried up already. Will pulling one of the fuses, or even disconnecting the Gem, keep things quiet until I can have a mechanic check it out? Wife has a major medical appointment in 2 days, and this is our only vehicle. We don't even use the 4wd.