The EDPs on most aircraft (well all I know) incl 757 are powered off by a solenoid. So when you select them off the solenoid is powered. It will burn out if left off too long.
Another B757 fact I learn't by experience.
Engine/APU bleeds.
There is an interlock so that, if the engine bleeds are not off, the APU bleed will not come on. You will see this in the bleed switches. If after shutdown there is no OFF light in one engine bleed switch, then the APU bleed will not open. The only way to overcome this is to manually wrench the valve closed with a spanner.
BUT, if you select the engine start switch to start, this interlock is overridden, and the APU bleed opens. This pressure will then push the bleed closed. (or start the engine if that is what you want)