Two quick questions

First: the diesel return line back to the tank. Where is it coming from? clearly its a low presure line. But how is that possible comming off the high pressure side? is there some valve hidden on the back of the block?

Second. There are three lines attached to the Cp3. one is high pressure supply to the rail. One is low pressure from the filter/water separator. What is the third for? if its to control the rail pressure, then what is the rail pressure sensor and FCA sitting there for?

I messed around with that last fuel line, and now i think im paying for it with a busted FCA.