Those home brew specials can be kinda icky. This bay be too obvious, but, is there an emergency shutoff switch on the PSU anywhere? paralell wire it if there is. Sometimes, it isn't as obvious. Get an old PC with an ATX supply. Pin #14 is the power switch control line through the motherboard. short it to ground, and the PC turns on. Remove short, and it turns off. There may be something like that. I dunno. Do you have any website links for the Arc PSU's? It could be neat to look at.
-Ben
