5 year old swift rio 320. I want to add 12v sockets for charging devices - all nice neat, as if part of original installation (OK so I'm OCD and I hate trailing cables!). My Rio 320 is surprisingly sparse, especially at the bed end. I want to wire directly into the Sargent (they have helpfully sent me a wiring diagram of the pin layout. So I know where the positive goes on there. BUT where on earth does the earth go to? The earthing points all seem to be deeply hidden. Does the earth have to be wired back into the loom somehow for the switching system to work?