Here's a picture of the wire wear as the bundle comes through the body to the rear hatch. Mike, you called it - it's exactly what you described.
The green/white wire is the only one I see that is fully severed (almost certainly the lead powering the rear wiper motor), but there are several others with worn through insulation. The bundle is very tight, short, and the wires hard to access within the rubber weather cover/grommet.
I've used all kinds of crimp connectors/jumpers in the past, etc, but I'm not sure what would be easiest here. Anybody have any suggestions on the best/easiest way to reconnect the broken wire, and also cover the connected wires that have worn insulation? Or is Mike's old fashioned way the right way to go? Thanks!