Re: really getting mad with xenon
As suggested, you want 2 relays for your head lamps one to drive each balast separately, ESPECIALLY with a shitty harness. If you had a nice well built harness with high quality terminals, relay connector, fuse holder and a legit relay and fuse (not the made in china crap that is in yours) and so on you would only be slightly safer. IF you want to use this harness, use it on your fog lamps but for your head lamps you really should have 2 separate relays. This way if you have a harness failure you still have a headlamp to get you home...
from there do as others have suggested and it will help isolate the problem.
Also mhardine, having to cycle the power to the balasts to get it to fire can also be an indication of a failing relay (thanks made in china relay).
2005 Jeep Grand Cherokee - Gone but not forgotten!