I replaced my alternator this summer because the diodes in the old one were bad. The replacement alt. is a ND that is identical to the OEM that came off of the car. My question is when I first start the car the volt meter reads about 14v and then after the car has run abour 5 min the gauge reads 12v. If I rev the car up the volts come up but when it returns to an idle they fall back to 12. This is especially noticable when the lights are on as they get dimmer at an idle and then brighten up at about 800 rpm's. The blower motor is the same way it slows down at a stop light and then picks up as I drive off. My idle is 650rpm. Is this normal for the fluctuation in voltage? I also replaced the battery when I replaced the alternator. The terminals are clean and the belt is tight. Any other ideas?