Vacuum pump wiring question ?????

I don't know anything about those pumps, but the stud on your starter relay is full time battery

Is it possible that they have a pressure switch to shut them off when they pump down?

The ONLY switched power under the hood is ignition power (the "dark blue" "run" wire, and you should not load it more than it already is, and besides, it is NOT fused.

Hook a relay to the starter relay stud, with a fuse to run the pump, and use the blue IGN lead to trigger the relay.

In fact, I use relays for both the fuel pump and ignition on mine.

You might want to read this:

http://www.gmcmotorhome.com/tech/vacuum_pump/index.html