You are right not wanting to disturb the wire harness, these can be replaced by re routing wires from the grey connector to the component. Snip the wires off near the connectors and splice in a new replacement wire.

#1..SB....Oil pressure sender (SB = black)
#2...Y....Water temperature gauge sender
#3...R....Alternator D+/61 (the thin red wire on the alt. back)
#4........Empty -- used on carb. models
#5..BL-Y..Starter solenoid (two thin wires there, note how they attach)
#6........Empty -- used on Diesel models
#7........Empty -- used on Turbo models
#8........Empty -- used on Diesel models

You should be looking for an updated harness at the bone yards or ebay for future replacement.

Check to see if Dave Barton has one.

http://www.davebarton.com/volvoharnesses.html

Dan