Tach Question...

ineedacottage

Seaman
Joined
Jul 12, 2006
Messages
69
Last year, I started having problems with my tach - it would rev up then slowly die. I checked connections at the control box and at the tach - pushed the 3 pin connector at the control box in to make sure it was seated properly. Same behavior occured with the tach.

I read on here that I can check the battery while under way to make sure the charging system is operating as the tach is tied into this somehow. Yesterday I measured the volts at the battery - I got 12.8 at home before we left. After a bit of a cruise on the lake I got a reading of 13.13 (this was with the motor off). Started the engine and the volts climbed slightly - I do not remember the exact volts at this point, but when underway (I would guess 2500 - 3000 rpm since the tach is dead) it climbed to 14.8 and would stay there. The battery was brand new last spring.

What would I check next? Is there some way I can check the wiring at the tach to see if the tach is shot or if it is the wiring somewhere...? Is there something else I should check?

Thanks for your help!
 

ineedacottage

Seaman
Joined
Jul 12, 2006
Messages
69
Re: Tach Question...

Anyone have any ideas...? I don't really want to buy a new tach and have the same problem, but I am not sure how to verify the wiring...?

Thanks for your help!
 

Barnacle_Bill

Admiral
Joined
Feb 8, 2004
Messages
6,469
Re: Tach Question...

You indicate that it was working properly at one time so that says that the wiring is correct. You also checked for loose or dirty connections. Your charging circuit appears to be working properly. That only leaves one thing, a bad tach. There is however a possibility that a diode in your rectifier is breaking down. To be sure borrow a tach and temporily hook it up or maybe you could find a shop that has one of those testers to test your tach.
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Re: Tach Question...

(Testing Tachometer With Water Cooled Regulator/Rectifier)
(J. Reeves)

A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).

A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.

However.... those watercooled regulator/rectifiers that are used on the 35amp charging systems (and some others) bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.

The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.

Remove that gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.

If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.

I've found this method to be a quick and efficient way of finding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disastrous consequences.
 

ineedacottage

Seaman
Joined
Jul 12, 2006
Messages
69
Re: Tach Question...

(Testing Tachometer With Water Cooled Regulator/Rectifier)
(J. Reeves)

A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).

A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.

However.... those watercooled regulator/rectifiers that are used on the 35amp charging systems (and some others) bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.

The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.

Remove that gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.

If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.

I've found this method to be a quick and efficient way of finding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disastrous consequences.

Is it possible for me to have a faulty regulator/rectifier and have my charging system working properly (according to my test above anyway)?

I actually saw that you had posted this else where and I was going to attempt this test in addition to the one I performed above, but I was a little unsure of myself. I am a little new to this and I think I found the wires you are talking about that lead to the stator/tach/regulator/rectifier, but I am not 100%. If I attach the wrong wire to the wrong terminal will I damage anything? I also was not sure if this is a redundant test if my charging system is working...?

Thanks for your help! It is much appreciated!
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Re: Tach Question...

That engine could have the regular water cooled voltage regulator/rectifier which would be on top of the powerhead just in back of the flywheel OR.....

It could have the smaller rectifier which sits just in front of a wiring terminal strip on the starboard (right) side of the powerhead. This smaller rectifier would have a cylindrical shape, about 1" in height, with a triangular base, attached to the powerhead with two screws.

Which do you have, water cooled or small rectifier?
 

ineedacottage

Seaman
Joined
Jul 12, 2006
Messages
69
Re: Tach Question...

That engine could have the regular water cooled voltage regulator/rectifier which would be on top of the powerhead just in back of the flywheel OR.....

It could have the smaller rectifier which sits just in front of a wiring terminal strip on the starboard (right) side of the powerhead. This smaller rectifier would have a cylindrical shape, about 1" in height, with a triangular base, attached to the powerhead with two screws.

Which do you have, water cooled or small rectifier?

I am not at home right now...but I know I traced some wires (yellow,yellow/gray,gray) from the terminal strip on the starboard side to right behind the flywheel on top. There were also some red wires but I did not trace those...this would lead me to believe that I have the water cooled voltage regulator/rectifier...I think? :)

Thanks again for your help.
 

ineedacottage

Seaman
Joined
Jul 12, 2006
Messages
69
Re: Tach Question...

I double checked...it is definitely the water-cooled one then because there is nothing like you describe in front of the terminal strip and some wires lead to what look like the regulator/rectifier (from some engine diagrams I have looked at) behind the flywheel.

So, is it possible for me to have a faulty regulator/rectifier and have my charging system working properly (according to my test above anyway)?

If I perform the test you have above and I attach the wrong wire to the wrong terminal will I damage anything?


Thanks for your help! It is much appreciated!
 

hoeser

Petty Officer 1st Class
Joined
Jun 18, 2006
Messages
253
Re: Tach Question...

Ensure the selector switch at the rear of the tach is in the right position. It should be at 6P. Try another tach maybe?
 

ineedacottage

Seaman
Joined
Jul 12, 2006
Messages
69
Re: Tach Question...

Ensure the selector switch at the rear of the tach is in the right position. It should be at 6P. Try another tach maybe?

Yeah, it is in the 6P. So according to my volt readings of the battery, my regulator/rectifier should be fine?

If so, that leaves the tach or the wiring...is there a way I can check the wiring with a multimeter at the tach or the control box to rule out the wiring before I replace the tach...?

Thanks a lot for your help!
 

hoeser

Petty Officer 1st Class
Joined
Jun 18, 2006
Messages
253
Re: Tach Question...

Hook up a multimeter to I(+) and G(-) on the tach with the key in the on position, ensure you have a working 12V going to the tach, if not, you have a power feed problem - wiring or otherwise. Not sure if you can really test the signal wire without a tach... I'm sure you can, but the easiest way to me is to just use a cheap tach.
 

ineedacottage

Seaman
Joined
Jul 12, 2006
Messages
69
Re: Tach Question...

Hook up a multimeter to I(+) and G(-) on the tach with the key in the on position, ensure you have a working 12V going to the tach, if not, you have a power feed problem - wiring or otherwise. Not sure if you can really test the signal wire without a tach... I'm sure you can, but the easiest way to me is to just use a cheap tach.

I have power...the tach lights up and the needle jumps when the key is turned to the on position.

I was calling the local dealer here about the price of a tach ($120 btw) and I mentioned my issue and he said the regulator could still be charging fine, but still cause the tach to not work - would Joe Reeves' method above tell me if the tach is shot or if it is the regulator...?

The cost of the regulator is $130 so I would prefer to only buy one of them :) ! Is it difficult to install the regulator since it is water-cooled?

Sorry for all the questions but I am new to this!

Thanks for your help!
 

Fl_Richard

Lieutenant
Joined
Jan 21, 2005
Messages
1,428
Re: Tach Question...

Sounds to me like the test Joe Reeves states would not be required if the rectifier could be diagnosed by the presence of a charging current.

I'd try his test. It sounds easy enough and it's decisive.
 

ineedacottage

Seaman
Joined
Jul 12, 2006
Messages
69
Re: Tach Question...

Sounds to me like the test Joe Reeves states would not be required if the rectifier could be diagnosed by the presence of a charging current.

I'd try his test. It sounds easy enough and it's decisive.

That's what I was thinking too...but being unfamiliar with this I am concerned if I attached the wrong wires that I might wreck something? I am pretty sure I found which wires he is referring to, but not 100%...

Since I need it running for his test, I'll have to wait 'til I am at the lake this weekend.

Although, I do have some water muffs, I guess I could test it on there...

Another question - if the tach works when connected to the yellow/gray wire and my charging system is working fine, could I just not leave it connected this new way? What are the ramifications of doing that...? Am I 'playing with fire' leaving it connected like that?

Thanks for your help!
 

Seasport

Chief Petty Officer
Joined
May 2, 2005
Messages
410
Re: Tach Question...

The gray wire comes out of your rectifier/regulator and has "cleaned up" pulses on it derived from the stator winding charging pulses (which come in on the yellow & yellow/gray wires). Looks like your charging circuit is working OK and you'd expect (but not guarantee) that you would be getting a signal on the gray wire. The best way to verify this would be to hook up an oscilloscope and have a look but I'm sure you don't have one of these! You should be able to measure a voltage (AC) on this wire if you have a voltmeter. This will change with revs but should be in the region of 5V.

You can use the yellow/gray wire instead of the gray because the tachs will usually also run off the "raw" pulses coming from the stator. This is a quick way of verifying if the gray wire output is faulty. I don't think you'll harm the tach by using this signal instead and this would be a workaround if the gray wire is faulty .

The other thing you could do is to take out the tach and take it to an instrument shop who can test it for you. If you have any friends into electronics they could put a signal generator onto it and check it out.

I take it that the tach used to work OK.
 

ineedacottage

Seaman
Joined
Jul 12, 2006
Messages
69
Re: Tach Question...

The gray wire comes out of your rectifier/regulator and has "cleaned up" pulses on it derived from the stator winding charging pulses (which come in on the yellow & yellow/gray wires). Looks like your charging circuit is working OK and you'd expect (but not guarantee) that you would be getting a signal on the gray wire. The best way to verify this would be to hook up an oscilloscope and have a look but I'm sure you don't have one of these! You should be able to measure a voltage (AC) on this wire if you have a voltmeter. This will change with revs but should be in the region of 5V.

You can use the yellow/gray wire instead of the gray because the tachs will usually also run off the "raw" pulses coming from the stator. This is a quick way of verifying if the gray wire output is faulty. I don't think you'll harm the tach by using this signal instead and this would be a workaround if the gray wire is faulty .

The other thing you could do is to take out the tach and take it to an instrument shop who can test it for you. If you have any friends into electronics they could put a signal generator onto it and check it out.

I take it that the tach used to work OK.

Yeah the tach used to work fine.

Thanks a lot for all the information - all the detail is great for a newb like myself.

So leaving it running off the yellow/gray wire (assuming that is what the problem turns out to be after I test it) would be ok? Or would it provide inaccurate readings on the tach because it is a "raw" pulse?

Thanks again for the help! :)
 

Seasport

Chief Petty Officer
Joined
May 2, 2005
Messages
410
Re: Tach Question...

Should be OK. It's more the frequency of the pulses rather than the shape. I have a feeling that it's your tach though but could be wrong. If you hook it up to the yellow/gray wire and all is fine then you know the tach is OK.
 
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