I just bought a 92 SC400 and I also have 2 of your 3 problems. My speedometer needle is completely out and tach sometimes flickers and I have moisture in the headlights.
The headlight issue was quick and easy to find, though I've not performed the repair yet. I feel like I've searched everything on the internet for the needle issue with little luck. I've found PDF's on how to remove the cluster and info on how to fix the digital cluster on the Soarer, (in case you haven't read it yet, the Soarer is the overseas version of the Lexus SC400, but it has a digital speedo). As far as repairing the needled dash you and I have, the only info I've obtained is painting them with flourescent paint (cool fix but not my style), or having them repaired by Lextech.org. I've not seen one post on any site that had anything less than great to say about the repair that they do, but I too am like you and really want to fix it myself. I can perform many a repair on electronics and PCB's but I'm not very good at troubleshooting the problem unless there is something obvious like signs of overheating etc. Hopefully we can help each other out and exchange info via this thread.
