1999 F-150 4X4, auto, 5.4.
electric windows won't work, transfer case won't shift, interior lights don't work. engine runs & trans shifts normal but obviously due to transfer case stuck in low I can't take it on the road.
I'm just wondering what all these systems may have in common. I swapped the acc relay with no help or change.
When I get in the truck things appear to work normal for just a fraction of a second (not long enough for x-fer case to shift) and then shut down until I reset the door and key again.

 

Bad GEM? The windshields on these trucks have a tendency to develop leaks, and the water drips right onto the GEM. Pull the GEM and inspect it for evidence of water and corrosion.

 

What is common is the GEM module located on the back of the fuse panel under the driver side of the dash.
To get the truck useable you could take the transfer case motor off and manually rotate the internal shifter rod back to normal 2wd position.
This should dis-engage the transfer case.
When you remount the motor be sure to rotate the electical connector board contacts back to the 2WD position.
If the front axle is engaged, the actuator can pulled out of lock providing the firewall solenoids are not trying to route engine vacuum to the actuator making it pull in again.
If you find the motor want to return engaged, remove the fuse that supplies it power
After all this, troubleshooting can begin.
The dash switch tells the GEM you requested 4H in the first position.
This normally causes the transfer case motor to run to the first position and engage the transmission via the link rod.
Then the firewall solenoid operates the accuator to engage the front axle.
Everything works in reverse when you go back to 2WD.
Only difference with 4L is the tranfer case motor runs to a second position and changes the shift sked for rpm vs up and down shifting besides a changing overall gear ratio.
Good luck.

 

Hey guys - I certainly appreciate the info. I was looking at the wiring schematics (like I should have to start with) and it does seem that the common item is the GEM. I don't think there is any water leaks from the windshield area (that I know of) but it's typically parked outside so weather itself may definitely be a contributing factor. I do remember GEM problems with a Ranger I had years ago also).
Fortunately it's not my primary vehicle (mostly my toy) so I'm not too concerned with getting it out of 4X low until I get the issue solved, (I can still use it around the property this way).
Thanks again, I'll keep watching for more info and update when it's fixed.

 

I see there are tons of used ones on ebay (and probably at local salvage yards) but my gut tells me to stay away from used GEM's.
I've looked around a little and the lowest cost I have found (so far) for a new GEM is autopartscheaper.com . Does anyone know if they are as good as they claim and a descent place to do business with? It does say their GEM's are the new & improved type so they'll pretty much last forever as long as they don't get wet.

 

Have you pulled your GEM yet and inspected it and the connector for corrosion?

 

Not yet, tomorrow is my first day off work since the problem started and that's the first thing I plan to do. I don't want to spend that kind of $$ before knowing for sure what the problem is. A full inspection is in order.

 

Yesterday everything worked fine (x-fer case, windows, etc) but I did take out the fuse box and GEM for inspection anyway and found no evidence of corrosion on connectors and didn't see any signs of water leak from windshield. Weather last couple days has been a LOT better than the several days prior so this may be a contributing factor.
Reading other people that have had similar problems I think I'll order a new GEM anyway.

 

Skydivemark don't be scared to order from Auto Parts Cheaper. I had to replace the GEM in my 98 and they were the only place I could get a NEW one. None of the Ford dealers within 50 miles of me could even get one.

They come with a complete set of instructions on how to replaced it. The only thing they don't tell you is that if you have big hands it's a real pain-in-the-*** to change. I had to get my wife to get her little hands in there.

Hope this helps
Bob

 

Hey, thanks for the info Bob. My local Ford dealer can get one but its nearly $400 so I'll definitely get it thru autopartscheaper.com. I don't see any significant negative comments about them.