The instrument panel sends power to the fuel shut off solenoid. The power goes from the instrument panel to the aux switch on the hyd control valve and from there to the solenoid. However there is also a wire from the instrument panel that by-passes the aux switch to send power to the solenoid. On startup if the aux handle is not in neutral, the engine will not start. My guess is after the start power is removed from the instruemtn panel, engine running, the panel switches to the axu overide circuit to send power to the fuel shut off solenoid as long as you are in the seat and the seat belt fastened. If this was not the case then the engine would die when you operated the aux hyd handle. The aux overide button on the instrument panel allows the instrument panel to continue to send power through this axu overide circuit when you leave the seat with the aux handle in an operate position. Leaving the seat with the aux handle in an operate mode will kill the engine if you do not push the button first...........The start interlock circuit will not keep the engine from starting if the engine is cranking because all parameters are met for th engine to crank. There are six power sources going to the instrument panel, whiich voltage input circuit controls what output circuit I am not sure. Since the engine dies when the lights are turned on, I would think the power for the fuel shut off solenoid, when the engine is running, comes from the run relay circuit.