How can I keep the rats from eating vehicle wiring?

you should get several bait stations so as to place bait around the property to reduce the population to begin with..I would definitely place a station around the cars too. Any rats that would be attracted to the bait placed out will be dead soon enough after eating the bait. There is a good repellent called Ropel that will keep the chewing from happening, but doubtful you can get it in all the places the rats can get and they will chew the unprotected wires.