When the engine continues to run with the key in the OFF position and I try to use anything that consumes power, headlights, horn, heater, it kills the engine instantly
This is why some of the guys are thinking bad switch or you got a small touch point going on somewhere.
Its providing just enough power to the coils with barely enough amps. Soon as you put power on something else the draw is enough to pull the load off that cross going on somewhere.
Since its most likely not a true hard contact or full wire it does not have the capacity to provide enough when the switch is off and your pulling load somewhere else.
