My alternator belt snapped a while back, but I fitted a new one and everything was fine. Last night however, driving in thick mist and rain, the batt light came on, and has not gone off since. It dims,and gets stronger when u flick wipers or windows etc. The belts still on and still spinning too. Any ideas? Tighten belt? Alternator knackered? Check the connections going to the alternator too, they appear fine and as they were before.