Before going through the hassel of wiring a ground to the battery, I looked in my owners manual and found out that there was more fuses than i thought, there was another fuse box on the passanger side that had the dash lights fuse and it was blown. On my car, there are several different fuses for the same things, you might double check every fuse. If it was a ground problem then the excess current going into the ground could have found it's way to your fuse block and blown one of the smaller fuses such as your dash lights before it grounded through the tires... not for sure. Perhaps another reason could be if your head unit is not very secure, and it moved a little and perchance caused your illumination wire to come in contact with ground if you didn't use that wire or just clipped it off...there could be several wires leading back to the lights that you might have just clipped off or something and if they came in contact with ground then your dash lights going out would most likely result, but in any case it would have blown a fuse, and if not then the only other thing i can think of is your bulbs actually burning out from an excess current before a fuse was blown. Good luck with this problem, I'm out of ideas.