Here is a real handy little gizmo, whether your fitting water spray to a car, want to have your existing waterspray at different boost setting and permanently moniterd or you want a boost alarm etc etc, thought it mite be usefull for someone 
http://cgi.ebay.com/ebaymotors/Boost-Pressure-Switch-For-Turbo-Water-Injection-
http://cgi.ebay.com/ebaymotors/Boost-Pressure-Switch-For-Turbo-Water-Injection-