In reality, it's up to you where this power comes from. But...
****For the most part though, people pull 24 volts off of the 2nd battery in your set-up.****
I've done some installs using the main car battery and currently have mine coming from a fifth battery in the trunk that usually runs my stereo. I've found that you'll have a longer play time if you pull that power from someone else. That second battery has a hell of a job because not only does it has to help the other batteries spin that pump motor, it also has to close all the solenoids and open the dumps whenever needed. I have 24-volt dumps but with a miss they've been opened with 12-volts for the past 12 years. As long as it's with a consistently charged battery (like the one under the hood) everything's fine.
And, yes, all of the "common" prongs on the switches need power.