I agree with U, poor schema
Y30 : Is a switch-over valve that protect the engine from overload.
When disabled : the intake manifold is directly connected to The ALDA "103" on the top of the IP. It enters in action if the waste-gate "=Boot pressure control valve"on the Turbo body doesn't open when the pressure reaches ~0.9, this event send an electrical signal (thanks to the pressure switch "S66") and cuts the flow to the ALDA that consequently stop providing diesel.
I didn't put names on the diagram, I supposed that everybody know how it works. ;-)
Please correct if Imy explanation isn't OK.