Most likely the ignition switch failed.
Other possibilities might be a broken or shorted wire from the switch ("S wire") to it's connection at the starter.
Should you attempt to replace the switch, the present push button "modification" may be taking the place of the original "S" wire at the starter's location.
In other words if you replace the switch, you may have to find the original wire to the starter (dangling/ chopped off) and reattach it when the modification is removed.
I made you a screenshot of the part (below), at this particular store it is an "order item" only. You can get it cheaper by looking up and doing your homework with promo codes. Looks like it exceeds the cut off price and shipping would be free!
Let us know how you progress.
The Medic
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Monday, July 2nd, 2018 AT 3:51 PM