TACH Sending Unit wiring diagram
I am with you Glow Worm. I believe that the module in my 66 Formula S is shot too. I have 12V at gray wire only (from dist.). There is an outfit that makes replacement boards to put in the original can. They also have some info. that may help to diagnose the problem. I will post it after I find it again. Where are you located in S. Ohio? I live outside of Charleston WV and my sister lives in Meigs Co. Ohio.