Gaffrig Tachs/Smartcraft acting up
 

I have 2002 Gaffrig Gauges and 496HO's and obviously smartcraft. The tachs run wacky they will jumo here and there and arent reading correctly. The previous owner had the same problem with different motors in the boat but says when he sent them to be checked that they came back fine. What could be happening? They do fog up a little sometimes... Moisture causing this? Thanks guys

No one has had similar issues?