Solenoid with an E ....
It's on the injection pump. There should be ONE leccy wire tagged to it.
IF (but ONLY if) there is live 12 volts on the solenoid, fuel will be supplied to the high presssure parts of the injection pump, and the engine SHOULD run.
If FOR ANY REASON there is no 12 volts supply to the solenoid, the engine WILL NOT RUN.
Turning the IGN key "ON" should apply 12 volts to the solenoid lifting the plunger valve against spring pressure, thus opening the fuel supply. Turning IGN OFF stops the 12volt supply so the spring pressure now CLOSES the solenoid valve which cuts the fuel supply, and the engine stops.
You can see why you are being recommended to check that single wire attached to the solenoid.
CharlesY