If you haven't already done this, I might suggest confirming if the issue is the TT or the TV. Have you tried "borrowing" a quick plug in from another trailer with 7-pin to see if the same fault comes up?
The wiring for the brakes is usually pretty obvious/exposed as well, you can visually inspect the see if there are any broken/unconnected wires coming from the backing plates of the brakes. They often use crimp on connectors back there, one might be off.
After that, it is either pulling out a multi-meter for self-diagnosis, or taking it back to the stealership.
2011 Jayco X19H (purchased 2015)
2008 Jayco 1007 PUP (purchased new, traded for the X19)
2012 Chev Traverse LT with TP