[slyalfa]

if the alt. is working it should be around 14.1V
the Alfa has a funky system where they feed the battery first then the rest of the car. so as a rule the more you load the system the voltage will go higher at the battery(over charging it)
as the regulation point is the dash light. but in this case it goes to the ARC control system. so if the voltage is not geting to that point right it will affect the alt working.

I guess the best way to test this is to pull the small wire off the alt. and read the voltage on it with the key on. it should read the same voltage as the battery. then if you ground that wire the light should come on in the dash.
if all that works then I would look at the alt. its self. pulling it out and cleaning it up and regresas the ball bearings and new brushes or a new regulator(comes with new brushes) will in most cases fix it.

now the short is a 2nd problem if still there.

also when you check the voltage on the small wire try it with the lights on and with them off.
the voltage should still be the same as the voltage across the battery.