The alternator stator is supposed to be insulated from earth.

Unfortunately, as the stator insulation degrades, the coil can become connected to earth. If this happens it will destroy your shiny new electronic regulator. The insulation in the picture is visibly damaged and eventually caused a short circuit...

So, check the stator windings are free of earth with a resistance check.

Disconnect the three alternator wires and check the resistance from any wire to earth. You should see a reading over 10k ohms.