tbc not working shows"trailer disconnected"

the tbc{trailer brake controller} has been replaced $543.27 at ford didn't fix the problem now they want $125.00 an hour to find the problem .I have also talk to ford customer service and they were no help I don't wont ot put in after market controller but am tired of dealing with this problem .we have had the the truck scan nothing showed up I just don't know what to do at this point . maybe a rag and some gas .other than this issue I love this truck it is a shame that this might get me to switch to a chevy