I have a 1964 Mercury 1000 that needs a tach. I also have an old Mercury Quicksilver tach, the type that is supposed to just plug right into the MerControl with a 3 pin plug. Well, for some reason that plug on my MerControl is just an empty hole. I want to run new wires all the way to the back for the tach. What does the tach need to be hooked to? I assume the 3 wires on the tach are signal, power, and ground? Where does the signal wire get it's signal?