OK. My boost gauge was installed (by someone else) and it didnt work. I have now replaced it and wired it up myslef. It works. But! I say but! Having been plumbed by the SAID expert, the gauge goes down instead of up. Being it is tapped into the vacuum line. Is this correct? It reads between 15-18 wich is about right. When I rev the engine the pressure drops to 15.
What is with that?
I am confused!

NOTE: It is a RaceTech gauge. Electronic type with the sensor under the bonnet.