I looked at several versions of the Owatonna/Mustang operators manual and I don't think they ever bothered to update it with a key switch starter. I have two versions of a key switch wiring diagram from the Deere service manual and service textbook for the 170. Of course, realizing the Deere products had a Wisconsin engine. I just joined this forum and it will not let me insert images, only url's. If you provide an email address, I will send them to you. That should get you where you need to go.
Good luck
Al Jones
Mustang 1700