Still working on troubleshooting the system, but I think I found a large part of the 12V problem. Not sure this would explain the 50A problem though.
But this one really torks me off because it was just plain negligent in how it was completed at the factory. Not withstanding using the wrong fuses, the box wasn't secured to the floor at all and was likely shifting a bit as we hit bumps, turns, etc. Which probably aggravated the breaking of some of the strands. But what really caused this was the fact that the white wire was cut much too short and had constant stress on it in a 90 degree turn. I also found nick marks from where the original installer had tried to strip the wire.
To top it all off the foil ducting was on the floor wrapped around these leads. I don't think this is how it was supposed to be installed!