Mice prefer not to chew on cloth covered wires. The way the cloth is woven causes it to snag on their teeth. Don't get me wrong those little bastards will eat anything. They would just rather eat those wax strings, plastic insulated wires and paper relay labels. Once they start gnawing on the cloth they usually get tired and move on to something easier before they do too much damage.
I say usually, because I'm sure there is probably somebody out there that had an entire machine stripped to bare wire by a family of them.