If i understand correctly, a pressure switch is used to prevent the NOS from switching on if the fuel pressure is below a certain point. I get the impression that the circuit to the arming switch (or something) is opened by the pressure switch. Well I want a pressure switch to close a circut. I need to figure out how to make an electric vacuum pump activate when the vacuum drops below a certin point. Any suggestions?

thanks. I have since found this
http://cgi.ebay.com/ebaymotors/aw-cg...item=597553217

and it turns itself off.

but i will use that as plan B.

You can get Hobbs switches in Normally open and normaly closed and in different pressures.
Try NAPA/UAP Parts stores