What is this electrical component and where should it be attached?

[markborley]

I bought my daughter a Polo that has just had a new clutch fitted. I have fitted a new timing chain and oil pump chain. I can see this electrical component (see photo) at the back of the engine but I don't know where it should be attached or what it does. I definitely didn't detach it deliberately when I was doing the chain replacement work but I might have accidentally dislodged it while I was grappling with the crankshaft sensor (it is close to the crankshaft sensor). What I think is more likely is the person who replaced the clutch either deliberately or accidentally detached it. I say that because one of the large bolts that joins the gearbox to the engine in this area had not been replaced fully (it was hardly screwed in at all) so he obviously didn't go back to this part of the engine when he finished the job. I'm only mentioning that so you know it might be something to do with the clutch replacement rather than anything to do with the timing chain replacement to aid identification, I'm not trying to shift blame onto someone else! So, what does it do, and more importantly, where should it be attached? Thank you.