The ignition interface was one of the first things that I thought of, does it go through some type relay to prevent operation of the TV when the engine is running?
Yes. The relay is activated by +12v from the "ON" side of the ignition switch, so it opens whenever the key is on (engine need not actually be running). Typically the relay is built right into the outlet, so the outlet has both 120v wires and 12v inputs.
Something you did either interrupted the 12v power or you did something to the 120v power to the outlet. Perhaps you removed the relay or changed its 12v source?
You can avoid the whole problem by plugging the tv to a different outlet.