Mercury tach problems

[J FISH]

Motor Mercury 125 1997/98
Tach Mercury

Question 1: How can one test the tach output (gray wire) of my regulator to make sure that it is working?

Question 2: Some one told me to splice into one of the yellow wires coming off my stator and it will give me the same readings that the gray wire would on the regulator? Any one have any experience with that?

Question 3: What settings should I put the tach on? 5P? This is what the original one was set to.



Background: I have 2 tach's and I can not get either one to work. I even bypassed all the wiring in the boat and connected directly to the Regulator to bypass any onboard issues, including ground and power wires.

I can not find any documentation on how to install an tach in a boat and certainly can not find anything on a Mercury tach.

Thank you all for your support.

 

[Barnacle_Bill]

Re: Mercury tach problems

Test your rectifier. Shorted diodes in it will keep your tach from working. Your tach should be set on 6P.

 

[J FISH]

Re: Mercury tach problems

Instead of a rectifier I have a Regulator and a 16 amp stator. All the diodes are internal in a sealed block so what does a guy do besides buy a new one?

 

[J FISH]

Re: Mercury tach problems

Well I ordered a new one off the net tonight. About half price compared to what the local dealer wanted.

This should fix my problem but can anyone else contest to what my tach should be set to? 5p or 6p on the back of a Mercury tach? Could this burn up the tach?

 

[ricksrster]

Re: Mercury tach problems

6P

 

[ricksrster]

Re: Mercury tach problems

Also besides the gray wire, there should be a 12v + from your ignition switch, a ground. some tachs have a post from an instrument light wire also. The gray wire at the rectifier actually does connect to one of the yellow wires from the stator. Your stator is 12 pole or 6 pulse. So you set your tach to 6P. All tachs are wired the same way now days. This link will help you:
http://ww2.tflx.com/PDF/99320.pdf

 

[Texasmark]

Re: Mercury tach problems

Think we have visited the following once before, several months ago. The boy's '95 150 V6 is set on 6P. Do the I4 cyl 125 and V6 cyl 150 have the same 12P stator?

JFISH, in answering your look and see question, the best thing would be a viewable Digital Multi Meter which has a screen on it similar to an oscilloscope; but much handier beins it's LED and hand held. I know Fluke Instruments makes them; or use an oscilloscope.

I don't know if the monitor (Grey wire) is prior to or after, the rectifiers in your rect/reg module. If prior to, you'd see a nice even string of sine waves which get closer together (shorter cycle time) as the rpm's increased. If after, assuming they use a FW bridge, you'd have a nice even string of half wave sinusoidal pulses.

I think if you are looking for a malfunction, that would be the best way to find it. If you had the data, an rms volt meter might be able to give you a number and that might be adequate for troubleshooting. However, nothing like a picture.

On the connections, his is Quicksilver and there are 3 wires on it besides the lightbulb power. I don't know how modern tach's count and display pulses. If I did I could help to identify the requirements (power/gnds, etc) required to make it work.

----------------------
One last tidbit. I have ordered a new tach for the boy's boat which is having tach problems also. People on here say that a rect/regl module going out shows up on the tach; others say that tach's have to be replaced periodically. Since he has 2 rect/regl modules on his engine we swapped them and the problem remained. So we feel that the tach is the problem. New one should be in the mail any day now.

HTH

Mark

 

[J FISH]

Re: Mercury tach problems

Thank you all for your help. Mark your info was great.

Rick, your link to Teleflex is exactly what I have been scouring the net for. It gives a very basic understanding of how a tach works and a simple way to test the regulator output to see if it is at fault.

Once again, thanks to all that contributed!

 

[Texasmark]

Re: Mercury tach problems

Well tain't that something. Thanks Rick for the site, and thanks J for mentioning it which cause me to go back to it and WALA, just what I needed too.

Thanks again,

Mark

 

[Texasmark]

Re: Mercury tach problems

Just took a quick scan of it and noticed in Fig. 3 the reference to Mercury is incorrect; at least for the 2 Mercs currently in my life. There is no provision from the stator (yellow wires) for tach on these engines. Rather they have a gray wire coming from the rect/regl for that. Have no idea as to what difference that makes to the tach.

They answered my question about # of poles being 12.

And for the record, the old tach was set up on 6P so I guess that reference is correct for Mercs, regardless of whether or not the tach signal comes directly from the stator (alternator) or the regulator module.

Also like the fact that they gave you some supplemental information. Very nice. Usually you get "do this, don't do that" and no one tells you why not, letting you make your own decisions !

Mark

 

[Barnacle_Bill]

Re: Mercury tach problems

I hope people read the instructions and not go just by the example shown in figure 3. It has the wiring for send and ign reversed. They did correct this in the instructions they send with a new tach.

 

[Texasmark]

Re: Mercury tach problems

Whoa, back the truck up.

bhile, what are you talking about? Would you walk me through that?

Thanks,

Mark

 

[ricksrster]

Re: Mercury tach problems

In figure 3 they show the wire from the send post on the tach connected to the ignition switch on position and the ign. post wire connected to the rectifier/regulator. It should be the other way around. I never noticed the error in the diagram before. Thank you bhile!

 

[Barnacle_Bill]

Re: Mercury tach problems

Mark, Rick hit the nail on the head.

 

[Texasmark]

Re: Mercury tach problems

Don't have it in front of me but it sounds right. The ign on would only be battery voltage, no pulses there. The rect/regl should be the gray wire and contain the pulses for the tach to count.

Thanks guys, glad you caught that.

Mark