If you do find that the GEM has gotten wet... Pull it, let it drain out any from the inside if it has any left..then bury it in a bowl of uncooked rice and tightly cover with saran wrap overnight. The rice will soak up any moisture in it. You may be able to save it. This I have seen a few times as well and it worked.

 

Where is the Gem located? What does it stand for?

 

It is located above the fuse panel under the dash.
If I remember right, GEM = Generic Electronic Module

 

Does anyone have a pic of location and or of it?

 

I dont have any pics but here are a couple of links that may help with descriptions. It can be a pain.
Hopefully someone else will pop in with pics.

Post #2 & 4
https://www.ford-trucks.com/forums/2...-location.html

Post #2
https://www.ford-trucks.com/forums/9...e-removal.html

Post #2
https://www.ford-trucks.com/forums/8...odule-gem.html

 

Chiming in, I may have this issue, need to figure out as well where the GEM is, we have had heavy rains here recently. I did change the headlights recently, but I tried putting the old ones back in, same thing, stayed stuck on. Not sure if I should throw a new switch on there first and see or what.

 

The GEM is the little black box behind the fuse box under the dash.

 

Here is the revised wiring diagram. I would check the wiring first for corrosion at connections, closed to grounds, and insulation detrition. The Low Beams are on separate circuits. One thing you didn't mention is does it have DRL's? This adds a little to the mix because there is also an Exterior Lighting Module which, when malfunctioning can do the same.

 

Ok, it's probably not the headlight switch, plugged in new one, headlights are still on, they headlights are even on when switch is unplugged. We checked all known fuses.
Dead end....