No power anywhere......

"It could"

So let's review so make sure I know "whut"

You say you have power to the ammeter AND at the alternator output stud?

And the headlights, dome lights, brake lights don't work? Nothing on the ignition switch works?

It HAS to be the "welded splice" I bet

Drop the column down pull the cluster. Untape the harness starting at the black ammeter, and look for the splice.