Are there no sign of a third connection, a field winding?
Normally the dynamo starts making power from the restmagnetism, this power is then lead to the fieldwinding, which becomes more magnetic, and the dynamo makes more power and so on.
Again normally, a regulator makes a connection to the battery when the voltage reaches a bit above 6 volts (the cut out relay) (here you can use your silicon rectifier). When the voltage exceeds 7,5-8 volts, the regulator will lower the voltage to the field winding.
