markfdr

It sounds that the ballast is not getting enough power, it might be a problem of loose connection or battery power. I would check the entrance to the ballast if there is enough power there and go till the battery.
I have quiet a lot of experience with HID's in diving, and when this happens it's usually the problem of the power to the ballast. If the ballast gets enough power, then usually its the problem is the ballast itself.
Hope it helps.