Here is a disassembly video. A loose knob problem can be tackled by pulling off the knob, encircling the cracked plastic with a zip tie (after putting Loctite glue in the cracks), pulling the zip tight. Don't lose the sleeve when you pull off the knob. But if this is not working for your setup, here is the disassembly, not your model but maybe useful: https://www.google.com/search?q=whirlpool+gas+top+disassembly
Can you get to the switch terminals and try jumping them out with a piece of insulated wire? That would tell you if the switch is defective (my suspicion). Please be careful not to touch any live terminals - only the wire insulation you use for the jumper.
