Thats exactly right shawn, the murphy switches "make or break" the ignition or run circuit depeding on whether or not the machines systems are within operating
parameters or not. On a welder its usually "low engine oil pressure" or "excessive coolant temp" that will shut it down. Thats why when you start these
machines you have to push a bypass switch that temporaraly sends current to the ignition or fuel solenoid so that the engine can start and achieve oil pressure
and close the circuit to keep the engine running. Obviously during a cold start up the coolant temp isnt an issue, but if it gets too hot it will shut the engine off.
These "engine protection systems" are very common on machines like welders, air compressors, generators, because there is usually no operator close enough to
see an idiot light or buzzer.