Flickering or pulstating Headlights

Well since I have had the car, changed the original alternator as the parts store said it was bad, the first one I got from the parts store I took back they couldn't find anything wrong with, but replaced it anyways. This is the second alternator, that I have put on it, maintains the battery fine. It has had a total of four VR'S the one the car came with electronic, two new mechanical, and one new electronic which is on the car now. Dah, this is like a soap opera. Thanks for all the help!