Re: wiring diagram for ignition switch
The primer solenoid is just a valve and does not inject or pressurize anything. The fuel has to be pressurized prior to reaching it either by cranking the engine which operates the fuel pump or by pumping the primer bulb on the fuel line. For that reason alone, it is generally more effective to hold the key in while cranking for a cold start.
The primer solenoid and the starter solenoid place a large load on the ignition wiring when operated together, so it is especially important that the wires from the wiring harness are in good shape and solidly connected on both of the solenoids - especially the ground wires.
Often a weakness in this function can indicate a poor negative battery connection or cable.