Can someone help,ive just fitted a digital boost gauge to my 05 wrx and it reads -1.0 and doesn't go up or down,ive got the wiring right i think,and have put a t piece between the dump valve and manifold,so though it should be fine but no,the only thing i didn't do was install what looks like a non return valve,should i have put this on and where would it go,

 

the non-return valve is going to be just a damper, if it was a non-return valve then you would only read vacume or boost and not both.

The damper works to smooth out the readings at the gauge/sensor so it's not hopping mad all over the place. Most likely you've got your wiring messed up just, double check the connections to be sure.

 

took it to the electrician today and diagnosed the boost sensor is faulty,now got to get demon tweaks to sort out another one ,thanks for your help