My 1987 Simplicity 4212 Hydrostatic with a Briggs 12hp I/C vertical shaft engine ran fine all last summer. I had it running fine last week and ran it for awhile. When I went to start it today, nothing happened... no click, engine didn't turn, starter didn't engage... nothing! I changed out the solenoid with a brand new spare I had on hand and still get nothing. I also checked all electrical connection points and safety switch connections and all are firmly connected. The spark plug is brand new too. I tested the battery and it is fully charged. I also tested power on the large pos/neg posts on the solenoid and am getting a full charge there too. I connected a jumper cable to the positive terminal on the rider battery and the other end to the starter motor post. The engine turns over at the same rate as when the tractor is started via the ignition key, but it won't fire. Absolutely nothing happens when I turn the ignition key though. Could the ingition switch be the problem or is there something else I should try? Please help!

Yes it could be your ignition switch but its also possible that one of your safety switches has failed. The seat switch is usually the first to go, check it with a continuity meter. By operating the switch you should be able to see if you can open and close a circuit. The circuit should be open when you depress the switch.

I have a simplicity 4212 hydrostatic lawn tractor it will not start