96 saab 900se turbo--Tachometer and fuel gauge problem

On my saab 900 some times tachometer works and some times it just indicate 0 RPM. Same thing with fuel gauges, sometime it shows full tank (when it is almost empty), somtimes it works good. Sometimes it helps then I put in Neutral when fuel gauge starts to show real level of gas.
Maybe somebody can help me with that?

You have an intermittent short somewhere in your instrument cluster, perhaps from a loosely fitted connection or a frayed wire touching on bare metal. The only way to solve it is to get a voltmeter and start testing out the entire system for continuity, though I'm betting that it's somewhere behind the instrument cluster and probally at the main harness connection there.