My tach is acting wierd, in the morning it will only read up to about 2000 RPM, as it warms up it will go as high as 3000 RPM and the needle sometime flucuates 500 to 1000 RPM in difference. I have replaced the tach with another and it does somewhat similar, but not exactly( only reads about 1500 - 1800 rpm, no higher), what are the chances it is two bad tachs.......

Any ideas if there is something else I should be looking at, where does the tach gets its signal from?

The car runs perfect, but I do not want to buy another tach if it could be something else.