Anyone up on KA alternator wiring?? It's a 1.3 duratec 53 plate KA and I think it has 'safe charging' on it?

The battery light is on peranently and the battery is ok. A common issues is mean to be the wiring to the alternator. We have three wires (orange, grey and blue) running to a plug on the alternator. If we unplug this the battery will charge but the battery light stays on. Plug it in and we get no charge.

The orange has feed,
grey -pressume is neutral
but the blue wire is dead??

I have checked the 3A fuse in the fuse box, this is ok, we have also taken the wires back about a foot from the plu end and all seems ok, no breaks but the blue is still dead.

We tried a feed on this blue wire but that jumps the charge up to 16v and still the battery light stay on.

Would it be likely a fault with the alternator or should there be a feed on this blue wire to the alternator and if so, where does the feed come from as I want to trace it back checking it's condition??

if it shouldn't have a feed, what does it do??

Help lol!!