I think you are right, a true factory tach does not work unless you get some sort of adapter or something. I think I have read that in other posts. But the newer ones that you can buy on ebay or parts houses will work. Mine works fine no issues. If I remember right there are 3 connections key power, ground and then the wire from the HEI tach to get the signal. Check on tach wiring install or something along that line instead of me trying to remember. That was a whole year ago (oldtimers desease). If you are going to install a tach in a non tach car it can be done without taking out the carrier. I did it in my 69. I might even have an extra template all ready printed out. There are tach templates in some of the posts. But just remember if you use them and are leaving the carrier in the car. You have to make a mirror image of them. The most important thing in cutting out the template is not the design of the tach body (since no one will see it), but the tach mounting hole location.Ted,
Everyone says the factory Tach will not work with an Electronic ignition due to how it recieves the voltage. How did you wire yours?