I don't know about fires in tractors, but I was informed last year that my truck insurance* doesn't cover mice chewing on wires. Luckily my electrical problem turned out to be something else, and covered by warranty.
Thanks Smokey, and Bubba, it definitely got me thinking, I called my insurance guy and decided to add complete coverage for the tractor. Tractor is in a shed that is far from mouse tight, I may start leaving the hood up too.