I was wanting to do the same thing this coming year and I was going to take a systems apprach to the tractor. The class I was going to use is Ag Machinery, and was going to cover tractor power for part of it. Within that I was going to have engines, hydraulics, power systems, and maybe electrical systems. Havent quite got the exact units done, but when I do I will send them if you want them.
John Deere has some good fundamental of operation systems books that go through all of the systems. There is a book for hydraulics, power trains, electrical systems, engines etc.