If you're not an "electronics expert" (and it sounds like you're not), what did your dealership have to say?
All it takes is a loose connection, a bad "crimp-on terminal" a staple through a cable or one of many other problems to make the system "not work".
If you do get "all the channels" when you connect "outside the KeyTV system, then it's fairly certain that the problem lies "within the KeyTV function.
Two choices, "tear into it and fix it" or "report it to the dealer and schedule an appointment". There is no "do these two steps and it will work"....
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS