My 260Z tach. is doing what it chooses to do ( goes form 0 to the end of red area after turning on the key-before turning to start; it then drops to 0 and sometimes it fluctuates. I have several extra transistor ignition unit (silver in color and (approximately 3" x 4") that I pulled off several different early Z cars. I am fair-good mechanical,but null and void in electrical and electronics--afraid of frying something. I need to look for them, they are boxed from my move from Texas to Las Vegas. Should there be a concern about whether or not they are the right one by, perhaps, an exact number on it or if they fits, try them? I have tightened every nut around the coil and little ceramic block (resister, I assume), checked the wire colors at that location and they seem to be correctly attacheched. lt seemed to have worked fine until I had my 260 engine installed with a used 260 engine about three years ago while in Texas, Any help would put me in monumental debt with you all; I would greatly appreciate it.