Tach and voltmeter needle jump

[Mark Noeltner <mark@xxxx>]

I'm hoping for a few suggestions for something that happened over the weekend.

My wife and I were on our way to a local event on Sunday morning when
suddenly the tachometer needle started jumping, then settle in about 1200
RPM too high. It continued to occasionally jump, then either go back to
normal, or back up to the same 1200 high a number of times as we drove.

Around the same time, but NOT at exactly the same time, the voltmeter
needle jumped a little bit. Unlike the tach it stayed at the correct level
most of the time, then would suddenly swing wildly over a 6 or 7 volt range
for a moment.

The two gauges did not seem to be doing this at the same time. The motor
was running very smoothly. And all the other gauges stayed rock steady.

The only common denominator I see on the wiring diagram is that they both
have the same ground and both get power from fuse #5. But so do all the
other gauges and instrument panel idiot lights and all of them were normal.

Any ideas of what to look at? I've already cleaned #5 fuse just in case and
it looked fine with no signs of overheating.

Thanks!

Mark