I have an opinion on how I think the typical Ford solenoid works, but if I'm out in left field, maybe another poster can set me straight. Here goes.. The positive battery cable (and other full time 12V reqirements) are connected to the supply side of the solenoid (one of the large posts). The opposite large post has the heavy starter cable connected. The small "S" post has the wire from the ignition switch which supplies 12 V to the solenoid when the key is pushed to the "START" position. The small "I" post feeds the coil with a full 12 V only during the time when the key is in the "START" position. So, we have 12V from the battery sitting at the soleniod all of the time. When the key is set to "RUN", the VR may "click" in response; but the solenoid is not engaged. However, the "I" terminal may now reflect 9 V as its in the ignition circuit being fed by the ignition switch through the pink resistance wire. When the key is set to the "START" position, the solenoid is triggered by the 12v at the "S" terminal. The solenoid then supplies 12 V down to the starter to crank the engine. The solenoid also applies 12V to the coil through the "I" terminal while the engine is cranking on the starter. When the key is returned to the "RUN" position, the solenoid disengages and the starter stops cranking. The 12V from the "I" terminal also ceases and the coil is again fed the 9 V from the ignition switch through the pink resistance wire.