Pull the handlebar cover off and unplug the connector for the brown wires on that side and see if that fixes it.
There are 2 momentary off switches, in the throttle block that the flapper pushes on when activated. I think one has to be open all the time to keep from grounding the motor out. If the sled is running, you should be able to push the front and the back of the flapper to the throttle block and kill the motor, but by having the rocking motion, it opens one simultaneously closing the other.
On an XLT I had, the plungers had actually worn through the contacts within the switches themselves and it would cut out at certain throttle positions. I unplugged it to make sure that is what it was, then replaced them.