2002 Glastron GX205 with a 5.0GL-B motor

[ddbyrd3]

I have a tach question. The needle in my tach tends to float every so often. I will be running down the lake and the gauge will be reading 6k then it will go back to the 3k or whatever I am running. I checked the ground wire on the coil, and I checked that the connections on the back of the gauge are clean and tight. Could this just be electrostatic build up after sitting under the cover while not in use???