Just about to have a bloody bonfire!!!

[Yendor]

Yendor, yes, as soon as the reg wire is disconnected the dash lights/volt gauge goes off

Your new alternator has issues.

You just need to make sure the White wire with a Red trace connects to the "L" terminal at the alternator and the White wire connects to the "S" and has 12 volts in it with ignition off.

I think this will be fine because you still have the original plug connected but it might pay to double check.

There is a good chance that your old alternator did have another problem that was causing the battery to go flat overnight.