Me too, @gunrunnerjohn, I see your signature includes MTH service, can I send it to Henning's? I won't cry too much about how long it might take to get it back. Right now, it just is what it is.
I think I found the problem. I don't think it was the black wire, I think it was one of the LED strands for the Christmas lights. I didn't see it broke, and the wires are loose and bare, where the black wasn't. I guess that's probably on a switch of some sort, and may have shorted directly to the frame. The LED's were on, so I can see where the new voltage source may have caused everything to go south.
Is it easy to just replace the logic board? I'm looking at it right now, and it looks like the worst part is handling the mass of wires. The board itself is just a few screws and JST type connectors. Does MTH sell that as a replacement part?