Intermittent Tachometer Readings

[OS2Dude]

We have a 1985 Catalina 30 with a Universal M-25. I am assuming the alternator and tachometer are OEM parts. The tachometer has been intermittent in its readings since we bought the boat, It will work, then not work, then work again. I can determine no pattern to its (not) functioning. The control panel was rewired as per recommendations about the dangerously undersized wires and 'trailer connectors' originally used, but the issue with the tachometer still exists. The wires all seem to be tightly connected, the new harness makes a broken wire unlikely.

I know next to nothing about engines and was hoping someone could give me an idea as to what the issue may be. What should I look for? Is it more likely the tach or the alternator?

Thank you

[model 10]

The tach people say it's almost always the connection in/at the alternator. Maybe solder it?

[jmiller148]

Had a similar problem. Mine did not seem loose at the tach, but since I cleaned and reattached it works every time.

[TurninTurtle]

Its going to be a bad wire or a bad connection...

Intermittent issues are annoying because they always seem to work fine when you are hunting for what is wrong.

I had similar on a bass boat. First the tach went intermittent, then the tilt/trim worked at the engine, but not the throttle lever's switch. Eventually I found the connection beside the power pack wasn't fully plugged in. Looked fine but was 1/16 inch from being fully connected.
But I didn't find it until something else went wrong...

[donradcliffe]

In many boats the tach runs off the alternator, which will stop putting out of the batteries are fully charged and there is no electrical load. Also, if there is a smart regulator, the tach will stop working for a while when the regulator shifts from acceptance to float voltage. Turn on a load like the running lights and see if the tach starts working again.

[model 10]

Originally Posted by donradcliffe

In many boats the tach runs off the alternator, which will stop putting out of the batteries are fully charged and there is no electrical load. Also, if there is a smart regulator, the tach will stop working for a while when the regulator shifts from acceptance to float voltage. Turn on a load like the running lights and see if the tach starts working again.

That is not what I thought was going on inside an alternator. The tach counts pulses of the poles inside the alternator and it has nothing to do with the charging.

[Paul L]

Originally Posted by Guy

That is not what I thought was going on inside an alternator. The tach counts pulses of the poles inside the alternator and it has nothing to do with the charging.

Don is correct. Many setups will not give tach pulses when the alt is not charging.

[Lepke]

Add a ground to the tack. If one exists, check all panel grounds. If you use crimp on terminals, I have found crimping to be unreliable and I have the expensive crimping tool. I solder after crimping.

[model 10]

Originally Posted by Paul L

Don is correct. Many setups will not give tach pulses when the alt is not charging.

I just looked at the Balmar manual and the tach counts the poles .

[CarlF]

Very common with some arrangements to have the tach "drop out" when the batteries are fully charged.

As suggested, it takes only a moment to rule this in or out. Run the battery down a bit or turn on some things. Nav lights alone may not be enough load. In my case, a two second hit of the bow thruster brought the tack right back.

[Paul L]

Originally Posted by Guy

I just looked at the Balmar manual and the tach counts the poles .

Take a look at the Balmar regulator manual. They briefly discuss the tach signal dropping out.