Steve, the overboost sensor is on the back side of the secondary intake manifold (also known as the recirculation valve housing, blow off valve, etc.) - it is on the left side, below the intercooler, towards the fuel head. The switch reads boost pressure, and at around 1.2 Bar, opens ground to the fuel pumps. If the wire comes off/partially off (bad contact) = no start, and if the switch goes bad, no start also. You can test it by unplugging the wire from it and grounding the wire end on a nearby, metal component (bypasses the switch and fuel pumps run).
Here it is - I pulled the pic off Google (squiggly yellow line was already there
). The switch is near the curved section of large hose and has a single spade on it.
