The rear defroster terminal, where the cable connects to the windshield came off. What do they use to attach this terminal to the glass? It looks like normal soldering stuff, but I tried with my soldering gun and it won't stick.

 

Did you clean it with flux first?

Do you have glass coverage on your truck?

 

If I remember correctly, the strips on the window are made of copper, hence why soldering them won't work. I'm also not even sure if you can weld/solder copper.....

 

check out a local parts store they may have some kind of metallic adhesive that will bond the metal together and still conduct elex, there is also a defroster strip repair kit maybe you could use this to stick things back together.
Have a IR gun handy to see how your repair went, you want to check the temp of the bond area, if its say over 150 degrees then the glass could crack as the resistance will be very hi and the rest of the defroster wont get as warm

 

sand with some smooth abrasive cloth or s.o.s put solder on the terminal heat a lot then put it on the window (the spot you just sand) hold it with your solder gun couple of sec and you should be good to go (don't heat it too much watch your backglass)