i have drawn up some diagrames to do this.it is not that hard to do, and you get a better and easier to read harness.. the one i made for my car is very much like a 84 system, i just am using a different cluster
why on earth would one need a new harness?
What is the problem? or are you building a car from scratch?
If you have had a fire, you could still maybe splice in new wires. To remove an old loom and replace with new you'd have to pretty much undo the whole car!
anyway, cable harnesses/looms came in various parts for the later cars, there wasn't a single loom like on old 60s alfas.
so you'd need to find the ECU/Injection loom, the instrument cluster loom, the centre console loom, and the main loom (contains fuse box and battery main leads and all the accessories etc)