I think the dome is constant +12V. I can turn it on when the car is off, or when I walk near the car it turns on. Your better with the cigarette lighter if you want it on when the engine on or accessory position.... Dash camera?? or reverse camera?? If Reverse camera you could tap into the back up light.Does anyone know the electrical scheme of the dome light panel ? I want a +12V wire only when engine on or accessory position to install a dash camera