Originally Posted by absentmathis

Yeah swapping sides for both bulb and ballast is a good measure. Yes - the kit I referenced is just bulbs and ballasts. Just make sure you get the right bulb type and it should be plug and play. I did just that on my '03 e39 and light output improved. The projectors and housings are really the bright spot that you don't want to change, although they also degrade with time.