on my 96 classic wrx im just away to fit a boost gauge. am i cutting a tee section into the vacuum pipe which goe from the boost solenoid to the actuator?

cheers

 

You'd be better off avoiding the boost control pipework if you can, especially if the gauge is a mechanical one with a long pipe going all the way into the cabin.

If you don't have a spare take-off on your manifold (check this), the better pipe to tee into would be your dump valve control line.

 

As above,