Hello Gentlebricks

Some time ago, a friend/tech was repairing a wire under the driver's side dash in my 240 and when finished,handed me a small "relay" (square box with two or three plugs on it) and saie, " I fixed the wiring but this fell out and I am not sure where it goes". (he is not Volvo-certified/trained). I drove a few das before I realized the cruise-control was not operating at all. I have looked in the Bentley but no picture shows where it goes. Can you tell me how to re-install it? Additionally, I have a blue similar-but-larger unit but can't identify. Is there a book or website I can reference the part number with and identify this part? Thanks for your help,