I fixed mines today, 3/17/2008. I bought a
99 Legacy Outback with-out inspection. I had to get this fixed. Its still not registered I've had it for over a week. My problem I discovered was bad grounding. Press the window switch up and down to see if the interior light dims. Its an easy fix:
1. Disconect the negative from the battery.
2. Take the dash out.
3. Atach a cable to the screw on the back of the speedo with a cable connector. The screw has nothing attached to it and is next to the speedo harness with the green/black cable.
4. Run the cable down to the open hood latch and ground it there.
5. Connect the negative on the battery tighten it start the car ride around and see if this worked for you also.
The reason to connect the cable there is that the problem might be that the speedo is not getting enough current or volts. If you take the dash or instrument cluster apart and take the speedo out there is a circuit board or what ever is called. The screw ataches where it says GROUND but there is no ground atached to it..? Hope this helps, if it does let me know I'd like to take some credit for discovering something. Thanks for reading.