!@VDC from TV
Based on what you have already done, lets give this a try.
FIRST things FIRST!!! Pull the TT's 30 amp fuse by the battery box, pull the shore power connection and unplug the TT plug from the TV.
Follow the black TT cable that hooks up to the TV, back into the electrical box (usually mounted on the frame somewhere, not sure about a 5th wheel). Open the electrical box and find the 12VDC lead from the TV.
Isolate the TV 12VDC wire from the wire nut that connects it to the TT's battery controller and TT batteries.
Protect the other wires from being able to short out to ground.
Check pin 4 of the 7 pin TV receptacle (just check it again, could save a headache) to make sure you have 12VDC. One more test on the TV receptacle, if you have a 12VDC bulb with leads on it see if you are getting a strong 12VDC from the plug. Not saying that somewhere on the TV could be a corroded connection (this will give you 12VDC with no amperage behind it).
Plug in the TT plug into the TV. Check the TV wire in the electrical box to see if you have 12VDC. If not you may have a bad or corroded plug/connector or no electrical connection on the wire from the TV (open circuit).
While you are watching the volt meter have someone wiggle the TT cable that connects to the TV (at the TV) to see if it may be a lose connection/wire.
This will at least let you know if you have 12VDC hitting the splice/wire nut in the electrical box. Based on the tests that you have already performed it may be an open cable or bad connector.
Just be careful. Let me know if this does not locate the problem, we can do a few more things.
2013 Jayco Eagle 284BHS
250Watt Grape Solar Panel, MorningStar MPPT 60 Charge Controller
1500 Watt Ramsond PSI, 2 Trojan T145 Batteries (260Ah)
2 - AirSight Wireless IP Cameras (used as rear view cameras)
EnGenius WI-FI extender, D-Link wireless (n) modem
MagicJack Internet Phone
2012 Ford F150XLT, EcoBoost w/3.73
157" Wheel base, HD Towing Package
Our Solar Album http://www.jaycoowners.com/album.php?albumid=329