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Author Topic:   Outboard Engine Tachometer: 1999 Yamaha Two-cycle Engine
Binkster posted 12-07-2014 11:00 AM ET (US)   Profile for Binkster   Send Email to Binkster  
I just installed a new Yamaha binnicle shifter, a new wiring harness, and a new key start with harness, all coupled to a 1999 C60 Yamaha 60-HP two-cycle outboard engine on my 15-footer. Next, I would like to add a tachometer. There are four unused wires coming off the key start harness: red, green, yellow, and black. I have a four-cycle engine tachometer. I'm assuming the difference between a two-cycle and cour-cycle engine tachometer only the poles, which are changeable. [The tachometer on hand] also has sender, ground, ignition, and light connections. Can I use this tachometer? Or, do I need a dedicated two-cycle engine tachometer? And, how would I wire [the tachometer on hand to the Yamaha engine]?


jimh posted 12-07-2014 12:02 PM ET (US)     Profile for jimh  Send Email to jimh     
On the tachometer gauge you have on hand, the wiring for the 12-Volt supply voltage, the 12-Volt common, and the Lamp Illumination circuit should be the same as on any outboard engine tachometer. There is little concern for those circuits and where to connect them.

The only real concern is for the connection to the SENDER circuit. On a two-cycle outboard engine the usual source for the TACHOMETER SENDER signal is from the rectifier in the engine' s battery charging circuit. The connection is usually made to a point in the rectifier that delivers a half-wave rectification of the alternator coil output. As you are aware, the number of poles in the alternator, the number of magnets in the flywheel, and the wiring arrangement of them determines the ratio of the pulsating DC output to engine rotation speed, and the typical tachometer has a calibration control to match the dial calibration to a particular number of poles.

In Yamaha wiring harnesses, the conductors are color coded according to the scheme I show at

According to that wiring scheme, the insulation color GREEN is used for tachometer signals.

Usually with a Yamaha outboard engine the owner's manual provides an electrical schematic diagram that identifies all the major components, the wiring colors, and the signal functions. Consult that diagram to verify the circuits and wire colors. The wiring diagram in the owner's manual should clearly show the wiring harness and the four circuits you have left over. If the function of the conductors is not clearly identified, you can trace the circuit and deduce the function from its connection point.

jimh posted 12-07-2014 12:03 PM ET (US)     Profile for jimh  Send Email to jimh     
I cannot address your question, "will the tachometer I have work?"

You should ask a knowledgeable Yamaha service department person about that.

jimh posted 12-07-2014 12:09 PM ET (US)     Profile for jimh  Send Email to jimh     
If you do not have the owner's manual for a 1999 Yamaha 90-HP, you can get an electronic copy. Visit my REFERENCE page on how to obtain electronic copies of outboard engine owner's manuals at

Follow the link I give there for Yamaha. At the Yamaha resource, locate the manual you need. I believe the manual you need can be found at lit-18626-03-35_916.pdf

Unexpectedly, it appears that in that publication no information is provided on the tachometer, nor is there a wiring schematic diagram. Most unfortunate! There was such a diagram in my 1987 Yamaha engine manual.

Binkster posted 12-08-2014 01:21 PM ET (US)     Profile for Binkster  Send Email to Binkster     
Thank you jimh for the color code schedule, and your input. Electrical/electronic stuff is my weak point. I'll take the 4 stroke tach out of the equation and use the 2 stroke tach that presently sits in my antique runabout and see if I can make that work. If money were no object, I would probably buy a plug-in Yamaha tach, and just plug it into the new harness.


jimh posted 12-08-2014 02:28 PM ET (US)     Profile for jimh  Send Email to jimh     
I really don't know if the tachometer you have on hand will work or not. You should get advice from someone with more familiarity with the tachometer you have on hand before you decide to discard it.
alfa posted 12-09-2014 03:11 AM ET (US)     Profile for alfa  Send Email to alfa     
Hi Rich--using a 4 stroke tach with a 2 stroke engine: maybe the tach will show twice rev's. Have a try.--Alain
saumon posted 12-09-2014 04:38 AM ET (US)     Profile for saumon  Send Email to saumon     
The GREEN wire coming from the wiring harness goes to the SEND input on the tachometer. The tachometer should be set to 6 poles for a C60 3-cylinder engone.
jimh posted 12-09-2014 09:56 AM ET (US)     Profile for jimh  Send Email to jimh     
I spent some time using GOOGLE to search for images of a Yamaha outboard wiring diagram for a C90, but found nothing. If anyone has a copy of the wiring diagram for a Yamaha C90 outboard engine, perhaps you could make a scan of it and send it to me. I will be pleased to post it here for future reference.
saumon posted 12-09-2014 12:16 PM ET (US)     Profile for saumon  Send Email to saumon     
If you're talking about the C60 (and not the C90), here's the wiring diagram. File=6b0a8e2c7cf863860536b74963ac2fa8

jimh posted 12-09-2014 12:33 PM ET (US)     Profile for jimh  Send Email to jimh     
Many thanks for that PDF document showing the wiring for a C60.

In Yamaha lexicon, the "Lighting Coil" is the source of the battery charging current. The coil that Yamaha calls the "Charging Coil" is not used for battery charging; it is part of the electronic spark generation for the engine spark plugs.

You can see that from the LIGHTING COIL, the circuit runs to the RECTIFIER/REGULATOR. The output of the RECTIFIER/REGULATOR is on three conductors:

RED = 12-Volt positive to charge battery
BLACK = 12-Volt common to chassis
GREEN = half-wave tap to send pulses to the tachometer on the main wiring harness plug from the engine to the remote controls

The signal on the GREEN conductor is a series of DC pulses. The frequency of the pulses varies with the speed of rotation of the engine flywheel. The tachometer is a frequency counter that scales the pulse frequency to engine RPM and displays it to the operator.

saumon posted 12-09-2014 07:43 PM ET (US)     Profile for saumon  Send Email to saumon     
I'm be no mean electrical expert but, thinking about this, there sould also be a testing method to determine which wire at the remote control send the pulse, using a digital multimeter that can read frequencies, right?

They can be bought for around $12 from ebay ( http:/ / www. ebay. com/ itm/ Mini-VICTOR-VC921-3-3-4-DMM-Multimeter-Poc ket-Digital-Multimeter-Frequency-lcd-k-/ 291223878318 ) and, let's say at idle an engine run around 1000 rpm, that's 16.7 Hertz (cycle per second). Giving the fact that the tachometer set on 6 poles divide the number of pulses by 6 to give the right rpm, I guess the measured frequency at the sending wire should be around 100 Hertz for an engine running 1000 rpm at idle and, at 700 rpm, it woulb be 70 Hertz.

jimh, is this right?

jimh posted 12-09-2014 11:44 PM ET (US)     Profile for jimh  Send Email to jimh     
It sounds right to me. Actually confirming it with a frequency meter would be even more interesting. I don't think any of my DMM's can measure frequency.
Binkster posted 12-10-2014 11:52 AM ET (US)     Profile for Binkster  Send Email to Binkster     
If that's a fact then my 4 cycle tach won't be accurate when used on my 2 cycle outboard even when set to 6 poles. Can it damage anything in any way to try it?


saumon posted 12-10-2014 03:31 PM ET (US)     Profile for saumon  Send Email to saumon     

I don't think there's 4-stroke or 2-stroke tachometers. Yours may be labeled like that but, as long as it has the # of poles settings, it's the same for both.

Have a look at this chart from Faria: . The same tachometers can be used for 2-stroke and 4-stroke.

So, to answer your question, no, it can't damage anything and will even read correctly, as long as it have the right settings.

What is, exactly, the brand and model of that "4-cycle" tachometer you have? Is this one designed for marine outboard applications?

Binkster posted 12-10-2014 04:00 PM ET (US)     Profile for Binkster  Send Email to Binkster     
The tach was used on a '07 Honda 50. Only markings on the tach that might be a brand name is CE 50703-203/09
It also says 4 cycle gas--neg. side mof coil
O/B W/alt--al;ternator
The alternator is now set for 2 poles.


jimh posted 12-10-2014 11:52 PM ET (US)     Profile for jimh  Send Email to jimh     
The alpha-numeric string with "CE" as part is probably some imprimatur of the CE Mark. It is a European certification mark. See about-ce-marking/index_en.htm

It is not a brand name.

Since outboard motors are more or less universally designed to run from 12-Volt batteries, you can expect that a tachometer for an outboard engine is expecting the tachomoter pulses to be in the 0-Volt to 12-Volt range. (Actually, the pulses are slightly negative, as I recall, an artifact of the rectifier.) So there ought to not be much difference between a "four-cycle" tachometer and a "two-cycle" tachometer regarding the voltage of the tachometer signal. I suppose some engine maker might have an odd way to generate the tachometer pulse and its voltage might be different, but, from what I have seen, outboard engines do not tend to push technology very hard, at least not older two-cycle engines.

That leaves the only difference likely to be the calibration settings for converting the frequency pulses to RPM reading. Usually a universal-tachometer will have a wide range of settings available, from say two to six, for calibration.

Again, I cannot tell you anything about how the tachometer you have on hand is going to work. You will have to tell us.

Binkster posted 12-12-2014 01:43 PM ET (US)     Profile for Binkster  Send Email to Binkster     
jimh, I think from what I have learned from this thread I will hook up the 4 cycle tach and see if it will read the RPMs of my '99 Yamaha C 60. However I won't be able to start the engine to check for a week. Will check back in with the answer then.


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