Hello mate

thats a wierd one, if the battery light stays on there must be a wiring fault then, the battery light has a switched ignition supply, and then is connected to the alternator, which when NOT charging is earthed (negative), but once it starts charging it changes to positive (and as you know the bulb wont light if both sides are connected to positive). Also the alternator cannot commence charging without the battery light, at a guess i would say you have connected the thin blue wrie to the wrong point on the alternator, it sounds like its connected to something that is part of the alternators body.

Let me know how u get on