It is likely that you either have a bad ground, or bad connection on the +12VDC side of the gauge.
The FIRST thing that I would do is to verify that the old, "plug-style" connection to the gauges has been retro fitted to the newer, "screw-type". See http://www.catalina30.com/techlib/wi...deInfoPkg1.pdf
and this; http://forums.catalina.sailboatowner...d.php?t=135558
If that is OK, then I would take an Ohm meter, and test for continuity to the ground (black [likely], or yellow[less likely]) connection at the rear of the panel, by shaking the wire. If this works, shake the wire at the harness connector, and again near where it ties into the ground for the boat. I'd do the same with the +12V (Red) wire, testing for continuity between the 12V breaker that powers the instruments.