Instrumentation Malfunction

1992 Cadillac eldorado 171000 miles.
Runs exceptionally well, but here recently speedometer and fuel gage stopped working.
Also buttons on panel, i.E. Information, data, reset buttons not working on panel.
Strangely enough tachometer is working.

Before I take it in for repair what should I tell the mechanic to look for. (4.9 v8)