[wiswind]

Verify the battery connections....including the connections down by the starter (prone to corrosion).
Then check/monitor the voltage at the battery.....it should be steady.
If the voltage at the battery is NOT steady, or is low, then you have a electrical supply issue......battery/alternator would be suspect.

If the voltage at the battery is solid.....then check the voltage someplace else......like one of the power outlets to verify that it is very close to what you measured at the battery.....and that it is ALSO very steady....
If the voltage is fine at the battery, but is low or bouncing around when you check it elsewhere, the problem is most likely a connection issue.

My point here is that if the whole instrument cluster is acting up, then the first place to start checking is the battery....then work out....verifying the stability of the power source.