Also, I noticed that 12-volt power is brought from the fuse interior fuse block, and I think it just occurred to me why the relay is needed.
The controller, solenoid and rheostat require or at least operate off of 72 volts. The key switch turns on/off power to certain fuse slots on the interior fuse block, in that power is passed to the fuse slot for the radio only when the key switch is on. The "radio" fuse slot, has a fuse in it, that also has spades that tap the power from one side of the fuse (I wish I knew which way this modified power tapper was to be inserted)... maybe on the side where there is no power once the fuse blows, or the other side (constant power) as if not on the constant side, that would shut down everything if that single fuse blew. I guess the constant power side.
Anyway, this power source goes to the Toggle run switch (from the fuse block). And I believe the reason "now I am getting it", that the cube relay is there, is so that 12 volt power can be passed to the cube relay (via the fuse block), which said relay then advances 72 volts to the controller, solenoid, and rheostat.
I am still confused why the key switch can't just be wired directly to the cube block. The wiring diagram (shown in the previous post) indicates a diode is needed, before the key switch, which I kind of doubt has been installed, so maybe the cube eliminates the need for that perhaps, because 72 volts is never passed through the key switch, which the wiring diagram suggests 72 volts would be, which makes little sense because the other 12 volt circuitry is dependent on the key switch. (Maybe the reason the wiring diagram just passes 72 volts through the key switch, as shown in the diagram, is because the wiring diagram is for a golf cart [using the controller] whereas this is a car, and other 12-volt accessories are tied to the 12-volt key switch, so sending 72-volts through the key switch would make little sense, given the already dependent 12-volt functions connected to the key switch.)
So, maybe I have answered my own question. And that is, the cube relay is needed to switch the 72 volts, on and off to the various components, while the key switch remains dedicated to turning on and off 12-volt power to the pre-wired accessories governed by the car's existing solenoid. And the only reason for the toggle switch (run/off) is to essentially give the user a means to turn off the controller, while still being able to leave the key switch on to listen to the radio, charge a cell phone, etc.
If I have any of this backwards, by all means correct away. I am just trying to figure out this car, I got, that came with no instruction manual. With your help, you have made it possible. Many thanks, again.