changing dashboard instrumentpanel?

Hi, folks..!
Have got a 1999 Caddy 1,9 Sdi with analog quartz clock where the tachometer should have been...
Anyone who knows if the instrument panels are interchangeable between models? What about the wiring and sockets? Do I have to pull new wiring before installing the new panel?
I also have some problems with the speedometer. It`s either working, or not. When it works, it works from the start till the end of the tour, and when it does`nt work it stays out of function all the time. It never suddenly starts working during driving, and the same whwn it works... It never stops working in the middle of a drive...
Someone who knows about these problems??