I am on an assignment to test the domain of input values of a tachometer, and what output (deflection) different values correspond to. In other words, what's the minimum and maximum signals and what does the curve look like? The trouble is I can't get ANY useful information. The tach has three inputs: Ground, +12V, and frequency. I have the output ground of the function generator connected with the ground of the tach (and the ground of the power supply), and the frequency input with the non-ground output of the FG. No matter what frequency I use, the needle on the tach does not move. What in the world am I doing wrong here? Can anyone describe or picture in detail what they would use as their test setup?