ugh that sucks. if it was a normal deck, it wouldnt have many wires, but since were dealing with a mach head unit and external mach amps that run on 9v system, its going to be a pita.
maybe chiltons/haynes has a diagram of the mach460 deck/harness. other than that, id say save the headache, and take it to a professional shop, might cost but it might be worth not going through the headache.