5-10 psi, idk because your modded. A stock GTP is around 7-8 psi.
With your flow mods and such it will cut down on boost PSI, but you still get the power because it flows better.
Splice the wire into a wire that always gets power when the key is on or buy a TAP A FUSE or ADD A FUSE, thing at a local auto store and use that on you radio fuse.