Just started today - when the door is closed, it trips the breaker. I do not know where the thermal fuse is to check it. I don't see any loose wires, and no wires underneath look corroded.

You will need a meter to find the grounded hot wire coming from the door switch. It is doubtful that you will be able to see it until you know which wire or switch to look at for a bare spot. Here are some books: https://dl.dropboxusercontent.com/u/...Dishwasher.pdf
https://dl.dropboxusercontent.com/u/...e%20Manual.pdf
https://dl.dropboxusercontent.com/u/...e%20Manual.pdf
It will be an easy job with a meter, but an impossible one without one. Get a good digital meter at Home Depot or Lowe's.