Replace the 7 pin....and work your way back to the front..It could be something so simple like a ground wire.....keep at it. You will find the fail. 7 pin plugs go bad all the time..when did you use it last? How did you know you were not getting power to the RV?...I'm stummped here...External charging wire? WHY? SO...you have 2x 7 pin connectors? My truck does....but you say your using the rear plug on the rear bumber? This is confusing...if I try to help we all need more detailed info. The TC power is hooked up where? Do you have a battery switch? Connected to the fire wall? For a second plug?
When you have two seperate systems that supply power to an RV it is common that the rear bummper plug will be hot while the rig is running but like mine it is split... When you turn off the rig, the bateries are seperated from the RV. I have a 7 pin on the front interior of my truck bed. I have a 7 pin at the hitch. The wiring at the bed connection is beefed up from the factory because I made that tweek to help make the batteries get more power when we travel.. I hope this makes sence..I was running dual 36 Interstates with a 100 watt sollar. All I needed. I am not going to rule this out...but have your alt checked..It is the prosses of elimitation...keep working you will find it!!!