Originally Posted by EOD Guy
"S" or "F" terminal on the starter should have 12v in start only, dead otherwise. This terminal gets 12v from the ing switch when the key is in the start position and makes the solenoid engage which in-turn makes the motor spin etc....
To check this correctly, you will need to disconnect the wiring to the + side of the coil.
If you leave the coil connected, that post will have voltage to it any time the engine is running or the key is on.
Disconnected from the coil-----you should be getting 12volts to the "I" terminal (or wire) while the starter is engaged----and nothing with the key off or key on and the starter not engaged