I`ve actually explained it slighty wrong, but the principle still stands; Where I`ve said the left line to the N75 is `vacuum`, it`s actually just atmospheric pressure. The other line to the N75 (boost pressure) comes from the compressor housing (or very near to it) which, if memory serves, is the red line. The blue line then goes to the wastegate actuator. In this diagram (courtesy of TDIClub) the two lines in question are; the light blue one on the left by the N75, and the slightly darker blue top-right going to the ECU, both annotated as `Black hose 4mm.
