Malfunctioning analog gauges

[jochburns]

Analog tach and volt gauges on 2003 Whaler are functioning erratically. Battery charging and starting fine. Volt gauge works erratically. Reads low or flat then appears to work normal. No pattern. Same thing with the RPM although will ocasionlly go up to @ 5-6000 when only running at about 3-3500 RPM. Any ideas? Checked a search for "gauges" and didn't really find a similar reference.
Any insight to the prob is appreciated.

[timebandit]

This a Merc Engine, I assume? A bad ground in the engine will cause this. The cannon plug in the motor screws up all the time on older Merc's.