Having acquired an interior light and a couple of door switches from the scrappy I discovered that whoever fitted the roof-mounted aerial had got it so that the stud holding the earth wire could short out the light while wangling it back into place. It would have been OK but while the two earth connectors had insulating sleeves, the live one didn't...thanks a bunch! Still, good news, I've found another place where water can get in. Bad news, I bet those two screws aren't going to give up without a fight...
