Kevin8520 wrote:
Sounds and looks like a bad 12 volt circuit breaker. Others will follow with additional answers.

Notice:
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Part 2: Got home, re-connected jumper, expected jack to work and instead, got nothing. Connected to shore power, still no jack, and now only appliances work in TT, not lights as previously before I did the jumpering."
He said that he re-connected the jumper and the jack did not work. May be a bad jumper. To diagnose the problem you will have to take a voltmeter and trace the DC path from the battery to the jack. Also read the battery voltage and tell us what it is.