# Tachometer signal **URL:** \ **Category:** MECHANICAL\ **Created:** [December 11, 2024, 6:44pm UTC](https://forum.oldboatshome.com/t/tachometer-signal/474 "2024-12-11T18:44:14Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Muze](https://avatars.discourse-cdn.com/v4/letter/m/9f8e36/32.png) [@Muze](https://forum.oldboatshome.com/u/Muze)\ **Post date:** [December 11, 2024, 6:44pm UTC](https://forum.oldboatshome.com/t/tachometer-signal/474/1 "2024-12-11T18:44:15Z")
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) ---
**Author:** ![Bilgerat](https://dub1.discourse-cdn.com/flex017/user_avatar/forum.oldboatshome.com/bilgerat/32/125_2.png) [@Bilgerat](https://forum.oldboatshome.com/u/Bilgerat)\ **Post date:** [December 12, 2024, 4:10pm UTC](https://forum.oldboatshome.com/t/tachometer-signal/474/2 "2024-12-12T16:10:28Z")
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. ---
**Author:** ![JimG](https://avatars.discourse-cdn.com/v4/letter/j/f1d935/32.png) [@JimG](https://forum.oldboatshome.com/u/JimG)\ **Post date:** [December 12, 2024, 11:58pm UTC](https://forum.oldboatshome.com/t/tachometer-signal/474/3 "2024-12-12T23:58:54Z")
Negative side of coil. ---
**Author:** ![DavidK](https://dub1.discourse-cdn.com/flex017/user_avatar/forum.oldboatshome.com/davidk/32/106_2.png) [@DavidK](https://forum.oldboatshome.com/u/DavidK)\ **Post date:** [December 15, 2024, 7:32am UTC](https://forum.oldboatshome.com/t/tachometer-signal/474/4 "2024-12-15T07:32:27Z")
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. ---
**Author:** ![Muze](https://avatars.discourse-cdn.com/v4/letter/m/9f8e36/32.png) [@Muze](https://forum.oldboatshome.com/u/Muze)\ **Post date:** [December 16, 2024, 8:15pm UTC](https://forum.oldboatshome.com/t/tachometer-signal/474/5 "2024-12-16T20:15:34Z")
![IMG_9707](https://europe1.discourse-cdn.com/flex017/uploads/oldboatshome/original/1X/f839eefabe1aeb3fde09f410ae4a45bc72c787b9.jpeg) 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. ---
**Author:** ![Muze](https://avatars.discourse-cdn.com/v4/letter/m/9f8e36/32.png) [@Muze](https://forum.oldboatshome.com/u/Muze)\ **Post date:** [December 16, 2024, 8:20pm UTC](https://forum.oldboatshome.com/t/tachometer-signal/474/6 "2024-12-16T20:20:25Z")
Oh forgot to tell, he old alternator has already been replaced by a modern type 12V