Confirmed in my rig that the isolator is not energized until after the engine starts running. Voltage on the ignition wire in the middle of the solenoid does not rise until after the engine starts.
Before that, as the key goes through its steps there are two loud clicks from below somewhere on the passenger side and then it starts. That must be the other solenoid I can't see.
Voltmeter on the house batts also shows no change until the engine is running--definite time delay there before voltage starts to rise.
Thanks everyone for explaining how all this works.
