well when i bought my car it had a new altenator in it but whenever i brang the rpm's past 4 grand the volt gauge would peg to 18 and the battery light would come on, so today i bought a new voltage regulator and now its sayin the volts are too low and the battery light comes on but i checked the battery and it was 12.6v and the alt output was 12.3v. 

and the headlights would get so bright