I have a '94 GT automatic it seems the car suffers from P.O.D. an had a aftermarket tachometer installed at one time, I know this because of the maounting holes an the blue wire leading from the coil. The question is my tach works very weird sometimes it works sometimes it doesn't sometimes its about right i feel an sometimes its way the hell off. It is the factory tachometer. Anyone got any suggestions on a fix or am i stuck choosing an buying an aftermarket one?