[QUOTE=SailorJo;13067]What is the most likely cause for a tach. in my 1984 C36 to suddenly stop working? Often recently when the engine was started, the tach. would not respond until I revved up the engine momentarily. Now it is not working at all.[/QUOTE]

Betcha have the boat plugged in all the time.

Your batteries are full and the alternator's regulator doesn't see a need to output.

Turn a DC load on.

Otherwise, you have a loose or broken wire usually at the back of your alternator.

SailorJo,
I echo Stu's comments. Most likely a loose connection. Check them all. Have you read the other posts on this subject? There are LOTS of them. The most recent is:
[URL]http://www.c36ia.com/forums/showthread.php?t=1700[/URL]

Sailorjo,
Im the one who started the thread that Tom listed and I finally solved my problem. Although my issue was not that the tach stopped reading any rpm, it was reading high. I fixed it by turning the ABCD adjusting scew on the back of the tach. I just turned it 180 degrees from its original stetting and back and it was then dead on. But I noticed that when I moved it to the (I think it was) "A" setting, from the "B", the tach reading went to zero, when the engine was actually turning 850rpm. I also noticed that after I initially turned the admustment screw, it became very loose and almost too easy to turn. It occurs to me that yours could have vibrated loose from the original setting and moved to the "A" positon. Check it out. If that's not it, then the loose wire idea sounds more likely.
Good luck.
Sam

A long time between SailJo's original post and my input...but hopefully someone will benefit along the line.

On Moon River, our 1986 C36 MKI, we had experienced a very erratic tach -- sometimes it worked, sometimes it didn't; sometimes it worked from the very beginning of the day and konked out later; sometimes it would kick in while maneuvering back into the slip. There seemingly was not rhyme nor reason.

The alternator seemed to be working fine - at least the batteries were being fully charged and the voltmeter was showing +/- 12 volts. My initial thought was that the tach had gone bad. And, I was hoping that I would only have to shell out for a new tach and not a ton of other "stuff".

Bottom line is that after performing various continuity tests I discovered that the tach, the wiring and the alternator were all fine. And yes the voltage regulator was taking care of charging the batteries, but it was NOT consistent in picking up on the pulses from the alternator that were to be sent to the tach. So for less than $50 incl shipping handling and taxes, I replaced the voltage regulator and again have an operational tach.

Moral of the story, dont jump to the conclusion (as I did) that simply because the tach is not working that it is the tach that is broke. Take the time to check the entire system.

Rick Caauwe
Moon River #550

When my Tach was acting up I experience the following.

When I first started the engine the tach wouldn't register. Then after running several minutes I would find it working. This sporadic behavior went on for several years. Since it always seem to "come back on" i didnt deal with it. Finally it got to where it was not working at all. A friend told me to check the wires on the back of the alternator. Lo and behold a wire to the Alternator had completely broke from its connector. I repaired the connection and tach works first time every time.

The hit and miss, originally, was more than likely, corrosion. When the boat sat the corrosion of a loose connection would set in. Once the engine was running enough the vibration created enough friction contact for the tach to work.

FYI -

My external Balmar regulator has a built-in delay feature to not energize the tach's field coil right away. That gives the engine a 'moment' to build oil pressure before adding the extra load.

You can wire the regulator to still give you tach readings even when the field coil is an open circuit, bit I have just not done that yet.

My tach registers briefly when I turn the engine on and then dies. Any ideas?

Enrique,
First guess is always connections. Check and tug on them all. Second guess would be corrosion internal to the tach. Open up the pod (engine off), and look at the back of the tach. There should be an selector for A-B-C-D or something like that. It may have a drop of red laquer on it. Note which letter it is pointing to. With a small screwdriver, move the selector back and forth several times, and return the selector back to the original letter. According to Dennis at Seaward Products, this cleans the internal contacts of any small bits of corrosion. It made my tach operative again after it got very flakey. Hope this helps.

Both times my tach became erratic I found the fan belt needed to be tensioned or replaced.