Battery Not Charging

[hedgerley]

Checking a few other things out on my 98 V8-GT before going after the alternator, especially all my earthing points. The battery light does not come on with the ignition, neither does it warn of no charge when the engine is running, but I know that the battery is not charging. The earth braid that runs from the right side engine 'cradle' was bright green and completely rotten - in fact fell apart when I prodded it. Given the engine starts and runs fine and all other systems seems to work OK without the braid in place, what is it for, protection only? The wiring diagram shows a seperate earth for the alternator and I know others have 'reinforced' this, put is this my problem? Is this the earth the alternator needs?

I am OK with the oily bits but electrics bamboozle me. Any thoughts out there, that I haven't already picked up?