Just curious, is the green wire from your tach making a connection at the black box on one of the wires leading to the coils? If so, that is the way we have been hooked up since I got the car.
I couldn't get a response from ProForm on my question about possible fixes. I don't think I will be buying any more tachs from them. In reality I probably don't need to worry about a tach much anyway. With the black box you kind of have a built in governor because they only let you run up to about 10,400 to 10,500 before the ignition starts to flutter. At least it works that way on ours.