Constant clicing from box going to induction manifold

Ok so I have constant clicking which I can ony explain as a induction resivour box. Its some sort of relay or sensor. Can u tellme what it is and is it suposed to be constantly clicking?

the image to where im pointing is what is clicking.

the image of the engine bay where the injector rail sows a plug not conected. There is no where ovbious where this should go. Should in be some where.

this is a 1.8 t golf 2000 any help would be great.