As per title, installed a boost gauge and spliced a T piece into the vacuum pipe running from the solenoid, to the EGR valve. Value only shows a negative value when throttle is at position 0 (no input from me), and at WOT, the needle moves to 0 psi. Am I missing something here? Tia

Why have you connected it to the EGR valve? Was this part of some instructions? Assuming it's a turbo boost gauge it will need to be piped direct to the induction system before the throttle body, if you go in after the throttle body it will read -1bar when the throttle is closed and not reflect any actual residual boost pressure. It's useful to know what residual boost remains after you take your foot off the gas, as this can give you some insight into what your actuator is doing and whether you need to consider fitting a dump valve.

8 hours ago, mr brightside said:

Why have you connected it to the EGR valve? Was this part of some instructions? Assuming it's a turbo boost gauge it will need to be piped direct to the induction system before the throttle body, if you go in after the throttle body it will read -1bar when the throttle is closed and not reflect any actual residual boost pressure. It's useful to know what residual boost remains after you take your foot off the gas, as this can give you some insight into what your actuator is doing and whether you need to consider fitting a dump valve.

I connected it to the EGR as foolishly I assumed that it wouldn't make a difference, on thinking logically, very little pressure would be required to move the egr...
So I should connect it to the vacuum pipe which goes to the turbo itself, that would make sense 🤣

A vacuum pipe to a turbo actuator (for waste gate valve or VNT vanes) will surely also read negative?

It needs to be in a boosted pipe.