ok I think I got it now.
If I have things correct.
The pressure port on the intake sends pressure to the ALDA, witch intern sends more fuel to the injectors.
If the turbo makes too much boost or the waste gate fails the over boost valve grounds and shuts the pressure to the ALDA and reduces the fuel to the pump ?

If this is correct I was thinking the switch over valve was always closed and power opened it. but in truth it closes when power is added.