Tachometer source of power

[MyPleasure]

Hi Fellas,
Our 36 Carver has twin Volvo Penta 740B gas engines. My port tach has stopped working over the winter, I checked the connections and everything looks good. Would anyone know if the tachs are driven from the alternator or the distributer?
Thanks for any help

[waybomb]

Power comes from the batteries.
The tech signal comes from the ignition.
Can you get to the backside of the tach easily? If yours are like mine, there is a screw that is used to select between 4, 6, and 8cyl engines. Turn that screw s number of times to all the settings, and then end it in 8. That may fix your issue.

[MyPleasure]

Thanks waybomb,
I can get to the back of the upper station tachs easily. I swapped the lower port tach to the upper port tach because the upper tach had stopped working, and now that tach has stopped working as well. I’m hoping that it’s not a problem with the wiring to the upper port tach.
When I swapped the tachs, I didn’t notice a setting screw for the number of cylinders, but I’ll have another look.
Thanks again!

[bud37]

Definitely check what Fred says and a question.....do you have an engine synchronizer gauge.......they can be connected to the tachs as well.