I have a similar problem. I described it in another thread:
http://www.peachparts.com/shopforum/diesel-discussion/337946-electrical-troubleshooting-85-w123.html

Car is W123, but probably quite similar wiring.

Lights did work for a while after replacing fuse, but tonight I once again had no dash lights.

There must be a short somewhere, but finding it is another thing.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5