From logic the voltage to the field is too high What can cause this? well if the D tag in the dynamo touches the field F tag then the dynamo output goes to the field and the voltage will increase as the revs do, Are you sure they are not touching in the dynamo? or being shorted by the cap? To prove this just remove the wire to the f tag at the regulator, the output voltage should drop to near zero when you rev up.
This assumes that the earth to the regulator has a good resistance free connection.