I realise this is a hard one but car running 11.6v across battery, pull lead off and car dies.

It's not charging at all. No light comes on the dash???? The Volt Meter in dash sits up just below 13v???

No fuses are blown, I've swapped out the relay.

Does this mean the alt itself has failed? Or is this still not a guarantee?

check voltage at the rear terminal of the alternator,it could be the main fuse has blown, if voltage is still low then yep dead alternator

Stop pulling your battery lead off to test your alternator .It doesn't work as a test.You will damage your alternator and blow the alternator fusible link.Doing the pull the lead off trick is very old school as in back in the days of generators being used to charge the battery.You have an alternator so you will be checking for battery voltage at the alternator B+ terminal ,battery light on the dash when you turn on the ignition which should go out when you start the car and a battery sensing wire going to the regulator and the earth side of battery light at the reg as well.Now go put the battery on charge ,buy a multimeter and a test light and a manual and do it properly.Hope this helps Kevman.

Cheers Troyman, checked voltage across the rear of alt and it's low

Looks like I'm in need of a new alt.

In that same vein, will a E Series Alt fit the AU (I know it will bolt on but connections, charging system wise)

no, it wont bolt on, e series have different mounting ,but a ba one will fit,,