Hi Gabriele, soory, I didn't see your message before now. My PSE setup uses what is called a "latching relay." This kind of relay holds power on or off each time it is switched, so when you pust the button, it keeps the valves open, until you push the button again. Go see my wiring diagram again, a regular relay won't work, it must be a latching relay. Good luck!
http://986forum.com/forums/boxster-general-discussions/50649-homemade-pse-version-1-0-done-behold-evan-sport-exhaust-pics-vid-writeup-%3D.html
