After all the tests known to man, with no luck, I decided to just pull new wires through. What a PIA. I drilled access holes that would stay hidden, but only one is visible. I will hide with a block off plate. I found the broken spot in the wire. It was visible. I ran one more continuity check on the piece of wire I suspected, and sure enough it was broken. It looked like it had been pinched at some point in time, and heat from resistance finished it. That would also explain why the copper wire was black looking. Time to run a new pair of wires and hook it all back together.