First prove it's the switch then either get a replacement or re wire if necessary , apply 12 volts to the selonoid terminal where the ignition switch hooks up , if it kicks in , you have a bad switch or wire then go from there
Any starter switch will probably work , all you need is 12 volts supply then 12 volts in the start position , you'll need to have a kill wire as well but get there one at a time .