Years ago I had my Gray Marine combinated rpm/ oil p/ amps/ temp meter rebuild from 6V to 12V and from mechanical shaft rpm drive to a electric rpm signal input. So far I never picked up and connected a electric rpm signal from the Gray Marine Fireball V8-225. For next season my goal is to have a good working tachometer. I only have a small note with remarks: 0 (0 rpm) = 0 Hz / 10 (1000 prm) = 100 Hz/ 20= 160 Hz/ 30= 220 Hz/ 40= 285 Hz/ 45= 310 Hz.
So far I found out there are 2 options: use the negative connection of ignation coil or the W connection of the dynamo (W pole= hard to find). My questions are:
-which option is preferabel
-do I need a interface for further adjustment or protection (if yes, what and how)
-how to make the electrical connection (does anyone has a E schema)
I can only offer what my Gray Marine 327 of 1966 vintage does. It takes the tach signal from the negative ignition coil to run the factory original tach. With a conversion, you may need an interface module to adapt that basic signal.
Negative side of coil.
You can certainly take it from the negative side of the spark coil. If you’re running electronic ignition that sometimes can cause problems. I believe you said your engines in 1966, which would mean it has a leece Nevel alternator. They have a neutral terminal on them, which will also produce an output pulse. If you’d like to talk about it more, please feel free to give us a call 201-445-8685.
Thanks for your answers/ advises. Have old skool ignition system. I will give it try by connecting the wire between the neg side of the spark coil and connector at the gauge for this purpose.
Oh forgot to tell, he old alternator has already been replaced by a modern type 12V