Connected my Boost gauge to the vaccum line off the fuel rail. Gauge is at zero with the engine off, when on the gauge goes to about 20 on the vaccum side and as I drive it goes up to 10 to 15. Bad gauge or what????? The car has a Saleen SC.

 

That's where I have my boost gauge tied in.... driver's side vac line running down the fuel rail. May be a bad gauge??

If so, I still have some Saleen gauges and the boost sender unit that screws right into the front of your blower.

 

When it goes to 10-15" vacuum, are you are WOT (or at least heavy on the pedal)? You shouldn't see any boost unless you're "getting on it". I can drive around town all week long and never see any boost... unless I want to. Stab the pedal and it jumps to 12 psi immediately.