1971 dodge fuse box??

You might not necessarily need to replace the harness. First, figure out what other crap has been added to the original wires and if that crap is still hooked into the harnesses (like an old alarm system). Check the splices because they could be corrosion points if not done correctly. If splices were added directly to the connectors, that might be more easily corrected.

Again, first determine what the added spliced wires are doing there.

Remember, though, you are dealing with 40+ year old wires and you can expect to see some degradation.