Easy enough to determine if the problem is on the Trailer or Tow Vehicle. Look up the pinout for the 7 wire harness on the internet (lots of good pictures available). Use a short piece of wire to jump the 12V pin on the trailer to each of the light circuits in turn. If only the correct lights come on then your trailer wiring is okay. If you get the weird effects, then there is a problem in the TT wiring.
I suspect the problem is more likely at the TV end though. You can use a multimeter to see if the only the correct circuits are being energized when they should be.
Either way, finding wiring issues like this can be a pain if the wires getting crossed in a hidden space. Have fun chasing it down!
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2011 Jayco X19H (purchased 2015)
2008 Jayco 1007 PUP (purchased new, traded for the X19)
2018 Nissan Titan Midnight Ed.
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