Model year/code of classic? Silly question I know but have you (a) tried disconnecting the switch altogether & (b) was the replacement new or used, as they are notorious for having a mind of their own. Also the reason I ask for the vehicle details is that from the 3.9ltr. an extra ECU was fitted (in the centre console) to prevent silly (little) buggers left alone in the car from choking themselves when they played with the windows.