hi y'all. really sorry but my curiosity has got the better of me here. does anyone know what the rear screen heater switch does in a doblo cargo van? when it's pushed a small yellow light appears on the rev counter and you get a click from under the dashboard as if a relay is operating but nothing seems to happen. I was under the impression that Fiat wouldn't fit something that didn't do anything and save themselves ten bob. maybe something is happening and i just aint spotted it yet, in that case apologies for my stupidness......