There should be a level at the engine label "STOP"... pull until engine
shuts off... unless you have one that has a turn knob on top of fuel filter
in front of engine... turn it in until engine stops... and turn it back out
so you can start later.

There's no wire to yank that will stop the engine. The engine is
normally shut down by a vacuum powered device on or inside the injector
pump.

Either the shut down device has worn out or there's insufficient vacuum
supply to the device due to a vacuum leak elsewhere - like a door lock.

One needs a vacuum pump / tester to find leaks and to test the shut down
device.