Strange Tach issue

[chautauquasun]

I have been looking for a solution for a tach that works only part of the time. This one baffles me. My tach did not work all summer. One day we got caught in a rain storm and I got moisture inside the tach lens. With the moisture in the lens, the tach started working again. A day later when it dried out...the tach stopped working. I have been thinking I had a bad ground somewhere but have never been able to trace it. This issue leads me to believe that maybe the tach itself if bad. It is the only instrument on the dash that does not work. Would all the instruments use the same ground? Any ideas on this?

[lively]

i have been looking for a solution for a tach that works only part of the time. This one baffles me. My tach did not work all summer. One day we got caught in a rain storm and i got moisture inside the tach lens. With the moisture in the lens, the tach started working again. A day later when it dried out...the tach stopped working. I have been thinking i had a bad ground somewhere but have never been able to trace it. This issue leads me to believe that maybe the tach itself if bad. It is the only instrument on the dash that does not work. Would all the instruments use the same ground? Any ideas on this?yes all the gauges use the same ground , usually u can verify wiring issues buy grounding the tack lead on the engine to the block itself ... Do you have points? Or electronic ign? Pcm 351?

[chautauquasun]

it is a 84 PCM 351w. I am running points. will the points have anything to do with it? I am thinking that because all the gauges work except the tack that it must be something in the tach. Maybe the moisture helped make contact???? doesnt make sense to me. Why would it work when wet but not when dry? Any thoughts?