You can't even get wiring harness from the dealer, so best bet is to go to junk yard and get one. You can't swap s4 and s5 (you can't use s5 wire for s4, visaversa)
And if and when you get the harness be careful removing them connectors as they are just as brittle as wires.
My suggestion is to replace that particular wire/wires completely and wrap it with thermal tape unless you want to cook that one, too
.
I know a guy who redone his harness completely with new wires. (told me took him 2 weeks)