Hi Dick, I think the reason for the diode was to prevent backfeeding to the rest of the electrical system, but I could be wrong. A diode is only a one way valve so if you add any circuts like for alarms , remote starts etc you can add a diode to allow the power to go only 1 way. Of course this only works on DC current. If you use 1 diode on AC current it will just cut the voltage in half. Allan R. 62 Imp conv as good as Johns, I wish it were even close