Adding a 12v porch light is mils to maybe 1A depending on the lamp that will have no affect on the problem. You really should go out the the pedestal with a volt meter and see if you can correlate the flickering lights to the meter. If all is OK its time to move toward the coach starting with the ATS. Its not the first time the lugs have loosened up and started arcing. If you have any 110 outlets NOT running through the inverter, measure there as well. The inverter also has a transfer relay that might be getting carboned up or loose lugs.