Definitely do the little bulb switcharoo trick. If it's the bulb, you'll obviously replace the pair, but I notice a lot of people that don't apply the same sense to replacing a shot ballast. If your kit is getting a bit old and one of your ballasts went, then you may as replace the pair. When I tried to replace only my broken ballast, I had an asymetrical light system. My new ballast warmed up faster and the light was brighter. Plus, my second one died a month later. If your kit is brand new and has a warranty, then you probably just got one unlucky ballast and you're best off just having them send you a replacement, but if your kit has some time under it's belt, you may as well upgrade. The thing about buying a pair of ballasts though, is that you may as well buy a kit. So truly, if you do find that it's your ballast, I recommend you just get a new kit. Especially when you can get a good one from DDM for $25 plus shipping. Then you know all your stuff is new, and you even get to change your bulb colour if you feel like trying something new.