I felt your pain! I guess a truck designed for Baja should have never been fitted with a defroster
Same issue here and when the dealer saw that the indicator on the control was not lighting, they said it was serious and may not be able to be under warrantee as they had seen it turned down in the past.
Being a tinkerer, I took the "cant be fixed" opinion and fixed that sh@&.
One important thing to realize that I found while debugging:
*My Defroster does not work unless the engine is running. Having the key on does not allow activation of the switch.
Things you need
•Good Contact Cleaner (Paid $10 for one at Radio Shack). It should be for electronics and it will gently dissolve grease and mild corrosion without damage to the contact points or melting/staining any plastics or film coating.
http://www.fordraptorforum.com/attachment.php?attachmentid=58670&stc=1&thumb=1&d=1419020390
•Compressed air and nozzle at least 100 PSI
•The ability to lower the back rest of your back seat (in super crew cab) see Squatting Dog's post
http://www.fordraptorforum.com/f10/rear-seats-17576/
1.Once the seat back is down (which a super cool thing to have anyway) open the slider about 2-3 inches
2.Find the contact points where the sliding portion makes the connection when the window is closed. You should be able to see them through the glass.
http://www.fordraptorforum.com/attachment.php?attachmentid=58669&stc=1&thumb=1&d=1419020390
3.Jam that air nozzle in the edge of the open glass and blow all the dust, dirt and crap out of channel and off the contact points
4.Now use the contact cleaner. If it came with the little red nozzle extender, put it on and shimmy it in between the open part of the windows and spray the contact points a couple times.
5.Let the solvent do its thing for a couple minutes. It will dissolve any surface corrosion, oil film or grease that is on the contacts.
6.Blast it again with compressed air to blow out whatever it had dissolved
7.Repeat steps 4,5 and 6 one or more times
8.Open and close the window a couple times to get the new clean contact points to seat
With the engine running, turn on the switch.
If it was just dirt and crud on the contact points, the selector should light up and your defrost should work.