Help...need tach signal info or assistance

[Bigprairie1]

Ok guys,
I am having no luck hooking up a 20 pole tach to my 90'/90hp.
I have a 20 pole tach (actually I now have 4-5 of 'em....different story that I will post separately) so I thought it might be the tach when I first tried this out.
Here is what I have done:
-GROUND: Ground wire from the engine to the ground stem/contact on the back of the tach. (this one should be simple......I think).
-IGNITION: 12V to the ignition contact stem on the back of the tach (I tried this both directly off the motor's circuit 12V/battery contact and directly off the battery posts 12v for this)
-SIGNAL: direct lead off the engine circuit tach 'signal' point to the contact stem on the tach. (shows/lists as a purple wire clearly labelled tach)
I got nothing on (3) different 20 pole tachs I tried. They are all set to the 20 pole setting on the back and I'm pretty sure that it is not the tachs. I get 12Volts to the tach.....but I'm not sure if signal is coming thru.
Is there a way to check for tach signal? Is there a better way to try this out?
What/how would you measure for tach signal with a multi-meter? Is there a better place to check for a tach signal up further in the engine? Can I try these tachs on a 4 cycle car motor to ensure it isn't them?....which I'm pretty sure of. (knowing that if they register and read the rpms will be off of course....but I don't if this is possible or not having never tried it)
Any help and info around this guys would be greatly appreciated. I was hoping to finally get a tach in my boat this year....but it ain't looking positive yet.
Many Thanks!!
BP

 

[john from md]

Re: Help...need tach signal info or assistance

The tach signal comes off of the stator and is an AC voltage. You should be able to us a voltmeter to see if you are getting anything at the tach itself. I don't know of the top of my head what the voltage is supposed to be though.

Is your battery charging properly? The reason I ask is that the purple wire is connected the same rectifier contact as one of the stator wires. The first place to check for voltage would be at the rectifier connections.

If you have voltage there, the next thing I would verify is that your ground is good.

Regards,

John

 

[Frank Acampora]

Re: Help...need tach signal info or assistance

Chech the rectifier. A bad rectifier will cause tach problems. Temporarily--just for test purposes, disconnect the ac wire and purple wire from the rectifier, clip them together, and see if the tach starts functioning. Start and run the engine for a few seconds only. Do not try to run and cruise like this.

Alternatively, if you have an extra, known good rectifier, replace the one on the engine.

Since the rectifier does not regulate, with everything connected correctly, the purple wire should have somewhere between 12 - 18 volts ac at idle.

 

[Bigprairie1]

Re: Help...need tach signal info or assistance

Good info guys, thanks. I wondered about the rectifier.
Here is another question: if the rectifier was not putting out a tach signal does that mean it is not functioning on all levels?
I ask because I've never, to my knowledge, had a problem with it or charging the battery, etc.
Regardless, as soon as it stops raining and warms up again for a couple of days I will do these checks and post some results.
All Good
BP

 

[john from md]

Re: Help...need tach signal info or assistance

The tach signal does not go through the rectifier. The wire for the tach signal and one of the wires from the stator are connected together at one of the rectifier terminals. It is just convenient to attach the signal wire to the stator wire at that point.

You can check for continuity from the wire at the engine to the wire at the tach to see if it is intermittant. Since the stator is used to charge the battery, if you weren't getting voltage from the stator, the battery wouldn't stay charges.

I would look that purple wire over carefully its entire length. Also, make sure you have a good ground.


John

 

[Bigprairie1]

Re: Help...need tach signal info or assistance

Ok, I checked both voltages coming thru this thing:
AC: 15.8 to 16.0 volts (this is inline with what you mentioned in your comments Frank)
DC: 12.6-13.0 volts (just the DC stuff measured there.
Now, There is no purple wire there but there is a grey wire that is connected to the DC- pole and from there it connects down onto the terminal strip at the 'tach' connection which has a purple wire output.
Does this seem right? Looks factory from my perspective?
Any more input on this guys is welcome and useful
Again many thanks
BP

 

[john from md]

Re: Help...need tach signal info or assistance

The tach signal wire must be connected to an AC pole. DC does not give you the pulse needed to operated the tach. It sounds like someone replaced the rectifier at one time and put the tach wire on the wrong pole.

I assume you checked the voltage at idle as the ouput from the recifier is too low to charge the battery.

I would move the tach signal wire to an AC pole. That should fix your problem.

Regards,

John

 

[Bigprairie1]

Re: Help...need tach signal info or assistance

The tach signal wire must be connected to an AC pole. DC does not give you the pulse needed to operated the tach. It sounds like someone replaced the rectifier at one time and put the tach wire on the wrong pole.

I assume you checked the voltage at idle as the ouput from the recifier is too low to charge the battery.

I would move the tach signal wire to an AC pole. That should fix your problem.

Regards,

John

John, that is very good and interesting feedback. That may very well have happened with the previous owner.
Both voltages were checked at idle....no throttling up at all.
With respect to the wiring, what...if anything would then the DC- connection on the rectifier have been connected to? (again it currently has a grey wire that goes from it down to the purple/tach terminal connection below...thus grounding out the tach....no wonder it didn't do anything). If this is just a DC ground...maybe its just grounded out to the motor? Or is just left as an empty terminal post? The wiring looks all complete there...no spare ground type wire or immediate connection nearby.
As well, in moving this grey wire over to one of the AC terminals...any problems or just double up on top of either of the (2) yellows that are currently connected to it?
Again many thanks!!
BP

 

[john from md]

Re: Help...need tach signal info or assistance

Most of them are doubled up on one of the AC terminals. Somehow you managed to get a ground as your battery is charging ok. When you move the wire, be sure to run a black wire to ground from the rectifier.

If you email me at johnandnanc182@yahoo.com, I will send you a picture of my regulator set up. the wires are mostly the same as for a rectifier.

John

 

[Bigprairie1]

Re: Help...need tach signal info or assistance

Most of them are doubled up on one of the AC terminals. Somehow you managed to get a ground as your battery is charging ok. When you move the wire, be sure to run a black wire to ground from the rectifier.

If you email me at johnandnanc182@yahoo.com, I will send you a picture of my regulator set up. the wires are mostly the same as for a rectifier.

John

Excellent (I love this site), on the way. The idea of finally getting a working tach (or actually any tach...given the fact the boat/motor didn't come with the optioned tach originally) is going to be nice.
BP

 

[Bigprairie1]

Re: Help...need tach signal info or assistance

Success!!....we have signal and we have a working tach! (or....tachs, I tested all of 'em, now I have to sell 'em off on Craigslist or equivalent I guess)
Many thanks for the input particularly John...you nailed it with that incorrect wiring find.
The only remaining trace to do is find why the (until now) unused purple tach/signal wire winding through the boat is capable of supplying a ground back to the rectifier...which worked. However, now I need that wire for the tach/signal up to the dash so I'll to figure that out.
It's funny the boat and wiring doesn't look like it was ever messed with or putzed as far as wiring goes. That said, it should all easier from here.
Again Many Thanks!!!
BP

 

[john from md]

Re: Help...need tach signal info or assistance

Glad to be of assistance. Pass it on to some other poor soul in distress.

John