There is supposed to be a tube running from a banjo bolt on the rear of the intake mainfold up to the rt side of the onverboost sensor. Then another tube runs from the sensor down to the ALDA on top of the IP. There is an electical plug in that has two wires and goes into the bottom of the sensor.
If that is really your overboost sensor then either there is no plumbing to the ALDA which would give you very poor performance at acceleraction, or someone found the oeverboost sensor to be plugged and just ran the pressure line from the sensor directly to the ALDA.