Their are two relays inside the voltage regulator. One controls the current to the field coils to regulate the charge voltage. The other simple turns on/off the charge light indicator. This relay gets it's signal from the "N" terminal of the alternator (the yellow wire of the two pin plug). This wire will be 0 volts ignition OFF or ON, and then be some postive voltage (above 6 volts) with the engine running.
Most likely it's your voltage regulator.