My 914 had bad wiring for the heat blower. When the 3rd blower motor died the wire from the blower thru the switch and all the way to the fuse panel melted. Luckily it didn't take anything else with it. Before I tried to run new wiring for that blower I sold it. Six months into new ownership, the new owner, a friend drove it for 2 weeks smelling fuel. Then it caught fire and burned to the ground. Not a particularly good idea to drive a fuel injected car smelling fuel.
After seeing your pics of the wiring looking like a snake nest, I would get a new harness. Just seems like it would be easier than what looks like is going to be a constant re-wire project.
Looks a lot like the wiring I found under the dash on my Rover. However, on the Rover the stock harness looks as if someone hacked it and a new harness would look exactly the same anyway.