41a Tachometer not working

[Pez Espada]

My Tachometer on my 41a stopped working. It first started flickering and then finally stopped completely. I have been down this road before so I bought a new one and have power to it, hour meter reads 00 and rpm needle is not moving after 15 hours of running. I checked all connections at the alternator. All connections seem to be fine. Not sure what to do next. Any info would be appreciated.

Thanks in advance, Zack

[NoSlack]

Zack

If the hour meter is part of the tach on the 41, and it doesn't advance with the key on, it's probably a bad tach gauge again.

The tach should have + and - terminals that go hot (12V) when the key is turned on. The other wire (grey)will be on terminal W, and that is the one coming from the alternator.

Also check the connections where the engine wiring harnes mates up to the umbilical cord and the other end of the cord behind the gauge panel. The plugs on that cord should have around 16 pins in them. If they get corroded, all kinds of thing start acting weird.

Mike

[Pez Espada]

Thanks for the comeback Mike,

I won't have a chance to look at it until Sunday or Monday. I will report back my findings.

Thanks again, Zack

[NoSlack]

I did a little research on VDO tachs and it looks like the wire coming up from the alternator is going to be a 12 volt square wave. That's going to be hard to measure with out and oscilloscope but you can try it with a regular volt meter. Set for AC voltage and measure between the G terminal on the tach and the negative. If you get something like 1.5 to 5 volts AC, I would say the signal is good.

One last thing to check. Make sure the alternator D terminal is well connected to the battery negative.

Mike

[hijole]

Ok, I'll be interested in this post.
My hour meter works but my tach doesn't always work.
I have been using the speed on the gps to guess my rpms.
Go get um Zack!

[Pez Espada]

Duplicate

[Pez Espada]

After a very frustrating time going back and forth from an alternator shop we were finally able to isolate it to a faulty tach terminal on the alternator. My brain is hurting after going through my entire wiring system on the boat. Double and triple checking the grounds. To give you an idea what I was going through. During the bench test, my alternator would check out perfect and then once i re-installed it and fired her up, I would get 0 reading on the tach terminal. Ater installing and reinstalling twice. Driving back and forth to the alternator shop with phone calls in between. We were finally able to get a zero reading on the tach terminal during the third bench test by rotating the terminal with pliers. Fixed the faulty connection, reinstalled, fired her up and a thing of beauty.

Thanks for the help guys, Zack

[NoSlack]

Way to stay after it and thanks for the update. Your persistence in finding the problem may save someone a lot of trouble in the future.

Mike

[hijole]

Zack, was the terminal post loose? Is it the wire with the 6mm or 7mm nut at the bottom of the alternator? I believe there are 2 of these wires at the bottom.

[Pez Espada]

Pepe,

The terminal was not loose and am not sure what wire it was. Zack