For patching the harness in my truck, I've done two things.
One, cut the section out and replace it with cotton wire ripped out of other old cars. For this, stealing the wires out of an old dash is great, as they are often in great shape, hot rodders are always throwing this stuff away.
Two, patch it with plasti-dip, or liquid electrical tape. I find that the stovebolt wiring always seems to have brittle or cracked insulation at the fender terminal blocks. After cleaning the contact points, I coat the last few inched of insulation with the goo. If you are neat, it doesn't look out of place. Well, if you use black!
