TBC (Trailer Brake Control Module) communicates with your PCM thru CanBus network, if you see Trailer Brake Module (TRM) Fault, that is just a generic fault to inform the driver and that means DTC(s) have been set, you will need a capable scanner to retrieve the exact DTC, the generic fault you see on dash doesn't provide additional info. A quick google search shows the following result:


Without knowing the exact DTC you are merely wasting your own time troubleshooting.
TBC/TRM, being a module, needs at least a power source (battery to fuse box to TBC) and a ground source, the module output to your trailer connector should also be going thru your fuse box, plus other linkage between your TBC and other components like TBC > TRM. To find out if it was a wiring problem the best you can do is to begin at the trailer connector, since you need to get a capable scanner to retrieve the DTC anyway, that capable scanner (bidirectional) should (no guarantee until it's plugged into your OBD2 port) also be able to perform a module reset. When it's a "module" that means it can communicate with the PCM, and that usually means you can reset such module. A capable bidirectional scanner, for example, Foxwell NT510 Elite, should be able to do all that.
Look at the DTC above, U0137 for instance, you can tell it's the PCM and TBC/TRM communication issue thru canbus. C2807 is obvious, short to ground between your TBC/TRM and trailer connector. You need to narrow it down, don't just expect disconnecting the battery ground can fix the error. When your scanner can do the reset, reset it that way.