Starter not turning off

I would access the ignition switch wiring to make sure there is not an aftermarket add-on like an alarm, and also make sure the wiring is not damaged. Next you can check the voltage on the red/light blue wire, there should only be 12 volts during the start position, if there is you can either disconnect the switch by unbolting the connector from it or clipping the wire a few inches back from the connector. You'll need to identify where your short to power is. I've attached some pics of the removal of the panels needed to access the ignition switch.