Ther are relays under the battery that get corroded. There is also a wiring harness plug that is between the engine and dash that may have bad connections in them. Check the black relay that is mounted under that battery tray. The fuses are also mounted below the battery. When I say under the battery tray I mean attached to the sheet metal that holds the battery, but they are visible without removing the battery. Who's bright idea it was to mount them where battery acid can get to them I will never know. I fought mine for several weeks when I got it before I could get it to run the starter. Can you hear a click when you turn the key ? if not then start at the relay and work backwards. Most of my fuse block was beyond repair and is now jerry rigged. I got a wiring diagram from the Toro site I don't recall if it was in the owners manual or a separate document. Also be sure it's not one of the saftey switches (Operator presence, PTO ,clutch
Does the test button on the dash work?