The little solenoid on the carburetor is called an "anti-dieseling solenoid". When you take power away from that solenoid, it sticks a plunger into the main jet of the carb and stop fuel flowing through carb, kills the engine. As for the fuel pump circuit, I'll try and walk you through it.
Ignition power comes from 87A of ignition relay, white/yellow wire. This relay is powered up by the platform and lower ingnition on switches. The white/yellow wire powers a number of circuits, including ingnition. It goes to terminal 87A of first fuel relay. You see this relay just above the Auto Choke Sol on the schematic. Notice, just before white/yel connects to 87A of fuel relay, it splits off and sends power to other circuits, one being the coil for the fuel relay. Power goes through the coil, and is looking for ground to activate the coil via the gray/blu wire. The gray/blu ties into the Engine Low Oil Pressure switch circuit, and finds ground because that switch is now closed because there's no oil pressure. Thus, the coil in fuel relay powers up and pulls the contact off of the ignition circuit on 87A and connects the contact with term 87 of fuel relay, the starting circuit. Therefore, when you turn the ignition "On", it takes away power from the fuel pump circuit. Once you hit the starter button, then you get power for the fuel pump from the start circuit via the contact connection in the fuel relay. Once engine gets running, and the low oil pressure switch breaks open, then the coil in fuel relay releases the contact and connects to 87A once again, sending power to fuel pump via ignition circuit.