hey my tachometer no longer works on my 87 gt. i found some melted insulation on the wires directly behind the intake. got that taken care of. fuses all check ok. still doesn't work. all other gauges are fine. when i turn the key on, the needle bottoms out and stays there. its been suggested that i replace the little circuit board that screws down to the back of the instrument cluster. i have one left over from when i replaced the cluster year or two back. just one thing, the little chip on the back of the boards are different in size. are the boards still interchangable? also, might there be any fusible links i'm overlooking? i was told the signal for the tach comes from the neg. side of the coil. is that correct? any ideas would be most welcome.