This guy sells harnesses, don't know if he has the one you need:
http://www.davebarton.com/index.html
1985 is one of the years Volvo used substandard engine bay wiring (Bosch); the insulation quickly deteriorates when subject to heat. That is why you will find the insulation totally gone on the wires that run close to the engine, worse where the temp is highest.
If you know how to make corrosion-free crimp connections, it might be most cost-effective to refit those sections that have suffered and leave the rest.