@windl
G4 TDIs no longer have this nipple!
The pressure is not measured using a hose in the engine control unit (ECU), but rather the sensor is directly integrated into the intercooler.
You will inevitably have to drill a hole somewhere to connect it.
That's the same as connecting an LDA (Light-Dependent Resistor), which has already been explained with pictures here.
@palm.
No turbocharger boost from 1Z to 2000?
However, Dashier looks different:
http://people.freenet.de/golf-schrauber/LDD-Umin.gif