Your OBP valve is bypassed, as evidenced by the picture you posted. But the electrical connector is in place. On top of the intake manifold near the rear of engine you'll find a pressure switch with a single terminal on it. That's the manifold overboost switch and it should have a wire going to the electrical connector on the valve. On the very rear of the manifold is a fitting with a tube attached. This is the banjo bolt. Follow the tube; it should be routed to the ALDA, a square thingy on top of the injection pump. Read my previous post for how the tubing is _supposed_ to be routed.

There's spirited debate as to whether the OBP valve is needed and those who tune their engines for max power would tend to bypass it. But for the most part, if you are going for original then you'll probably hook it up. If you attach it you'll want to make sure the banjo bolt is removed, cleaned and re-installed. Same for the OBP valve. Until you're ready to dive into the circuit, though, feel free to leave it alone.

__________________
mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)