According to the Service Box, you have to lower the window 2/3 of travel, remove the door card and plastic seal and prise the window glass out of the mechanism. Then suspend it in the raised position with (very) adhesive tape.
Then you can either drill out the rivets holding the regulator in place (maybe replace with screws when refitting?) and remove it to replace the wires, or you can try doing it in situ, but I'm not sure how easy that would be.
You probably need to disconnect the loudspeaker and remove it complete with support bracket.
New wires are available on eBay, e.g.
here.
Good luck, and let us know how it goes.