congrats; you have the 91-2 Yazaki speedo which is a known problem. There's some info in the FAQ, mostly you may have a hard time. Many speedo shops have been consulted, most tell you up front there's nothing they can do. There is one shop in SoCal that gives a warranty for about $300. Good used are hard to find.
One guy in WA made his own new cluster, yes the complete cluster with new aftermarket gauges and lights. It's remarkable.