Why my truck will not turn off

Because you left it running?

You have an auto start that bypasses some factory security sometimes they get stuck in a loop use your fob emergency button this will kill it then you get to enjoy the horn until you can get the thing to quit honking go to the shop that installed your autostart and have them reset it out of the loop

I am assuming you are turning the ignition switch and everything else shuts down but not the engine.

If so, it is a fuel shut off solenoid issue. It is likely broken (spring inside) or the cotter pin fell out, somehow, and the linkage from the solenoid to the valve is disconnected.

The solenoid is on the driver's (left) side of the engine under the intake manifold. There is a "hole" in the mess of wire loom, manifold and plumbing you can look through and see the solenoid. Stand about at the battery by the fender and look down there. The solenoid is just about vertical with the operating rod pointing down... reaching in there you can feel the rod sticking out of a rubber boot. If the cotter pin is present you can see it and feel it. If no cotter pin, feel around for the end of the shut off rod and push it down to shut off fuel.

Sounds like bad switch if a stick let out clutch to die out then take off pos bat terminal until fixed

Switch is bad!