I have a 2004 A3 3.2 Quattro which has developed a fault which is really bugging me. My rear light cluster lens was slightly cracked and had let in some water and so I removed the cluster to seal the lens and replace the reversing light, which had blown. At this point, no bulb blown warning was showing on the dash. When I removed the bulb I tested it and found that it was working fine and so I cleaned the terminals and replaced the whole unit. Upon doing so, the dash showed a blown fog light. The cluster was removed again, all bulbs tested and all were working. I replaced the whole unit again, and still the dash showed a blown bulb but all bulbs are working. Any ideas?