I deal with rodents in cars at least weekly for work. Car companies told my company that the wires have fish oil in the casing and that's what they're chewing for. I have a hard time believing that since fish oil is crazy expensiveRats eat wiring harnesses here. The newer wires are soy based insulation that they like. Orange or peppermint oil repells them.
Spraying the whole engine compartment with wd40 does a pretty good job of keeping them away and makes everything look nice. They'll usually start to nest in the air filter before they start chewing the wires


