Tach problems(erratic readings) help

[bigeasy1]

It's has to be something in the wiring or a electrical issue of some sort,as I set the gauge to 8 cyl when I installed it,and it had been working fine.The gauge is only a year and a half old with very few hours.
The odds that the gauge is bad I think are very low.I'm going to have to check out all the wiring and follow it back to the engine and harness.