Re: Motor wont shut off
Disclaimer - I'm not a mechanic.
Check your ground connections in the ignition circuit. It could be in the switch.
If I remember correctly, the off position of the switch shorts the ignition to ground, much like on an old lawnmower, which had a metal band bolted to the case(ground) that you touched to the spark plug to stop it.
Look at your ignition switch in the control box and find the wire attached to the case (ground). Find the other end of that wire through the cable to the motor and check continuity.
I bought a used motor once that wouldn't stop. I found that there was no continuity through the ground wire inside the cable to the motor and just ran an external wire to replace it by spiraling it on the outside of the cable.
It's a lack-of-ground problem IMO. It could be in the switch, as you suggest, not making the ground contact. You'll have to troubleshoot with an ohm meter to find out where you lose continuity to ground.
