The 2004 + MY trucks ( excluding the 2004 Heritage and Lightning ) have all the fuses and relays installed in the CJB ( aka Central Junction Box / passenger compartment fuse panel ) from the factory, unlike the 97-03 MY trucks ( and I would guess the '04 Heritage and L ).
If you do not have power at the trailer tow battery charge pin, that is Fuse # F106 and Relay 05 that control that.
I see a post about how you checked the fuse F106, how did you check the fuse ?
Are you are testing the trailer tow battery charge circuit with the key in the run position ?
It is only hot with the key in the run position, accy will not activate power to the 7 pin trailer tow adapter.
If you pull Relay 05, you can test Fuse #f106 to the relay by testing with a meter the pin connected to it.
Terminal 30 to ground with a meter ( ground lug in the lower right hand corner of the fuse panel ) should have + 12 V on it, if not, Fuse 106 is bad.
If you want to test the wiring to the trailer tow 7 pin adapter, jumper in the relay socket as shown above, and this will put +12 to the 7 pin trailer tow adapter without the key in the run position requirement.