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ContinuousWave: Small Boat Electrical
Yamaha Tachometer Wiring
|Author||Topic: Yamaha Tachometer Wiring|
posted 05-19-2007 11:35 PM ET (US)
I have a 2000 plain jane 30=HP Yamaha and want to wire a tachometer to it. I have a Yamaha tachometer and the dealer said he could do it if I brought it to him. I can't believe it can be that difficult to do myself.
posted 05-20-2007 08:59 AM ET (US)
It is not difficult to connect a tachometer. There are just a few connections. Boat owners have installed millions of tachometers.
Describe the terminals on the tachometer for us. Tell us if they are binding posts or if there is a connector. Describe the wiring harness from the motor. We will help you if you give us this information.
posted 05-20-2007 05:18 PM ET (US)
I have two tachs, a Yamaha and a Mercury. The Yamaha has a 4 pin (female) plug plus a green wire and a black wire on the upper left (looking at the rear of the tach) exiting from a potted hole and a black wire and a blue wire exiting from a rubber cover marked N461A, whatever that is, on the upper right. The four wires have male bullet connectors. I think the plug wires must be for the oil level and whatever and the green and black for the light.
The Mecury tach is much simpler. It has terminals marked Lt., Ign. Gnd. and Send. No oil level or anything.
The motor is another matter. It is a 30HP manual start w/o T/T. I can only see two wires not connected to anything and with female bullet connectors.
posted 05-22-2007 01:05 AM ET (US)
I installed a new digital tach / trim / hour meter on a Yamaha F60 and the entire install took 30 minutes and worked perfect...
posted 05-22-2007 09:25 AM ET (US)
Generally a tachometer gauge will have four connections as follows:
IGNITION--a source of 12-volts from the vessel engine ignition switch which is supplied in the ON or RUN and START positions of the ignition switch. This is typically a wire with VIOLET insulation. This powers the tachometer.
GROUND--the 12-volt battery minus terminal. This is typically a wire with BLACK insulation. This is part of the tachometer power wiring
LIGHTING--a source of 12-volts which is switched on when instrument panel lighting is desired. This is typically a wire with DARK BLUE insulation.
SENDER--the tachometer signal, a variable frequency pulse train typically a square wave which is clamped at the battery voltage. This is typically a wire with GRAY insulation. The frequency of the tachometer signal varies in proportion to the engine rotational speed as determined by the number of poles in the alternator windings of the charging circuit. The tachometer is often derived directly from the battery charging circuit and consists of a halfwave rectifier tap in the alternator output. The calibration of the tachometer has to match the number of poles in the alternator.
The above reference to color of wiring apply to American-made motors which follow the recommended color codes. Motors made by Japanese manufactures often use very different color codes. There is a list of color codes in
In the case of your Mercury tachometer, I can interpret the terminals as follows:
Ign. = IGNITION
Lt. = LIGHTING
Gnd. = GROUND
Send. = SENDER
For a comprehensive explanation of how the alternator works, see my article at
If you are unsure of the configuration of your alternator with respect to the number of poles, there usually is a reference to calibration of the tachometer supplied with the device that lists various models of outboard motor and the proper setting to use. If you do not have that literature you can test several settings and observe which one gives the most accurate readings.
posted 05-22-2007 09:36 AM ET (US)
To connect the tachometer (either the Mercury or the Yamaha) you will connect the GROUND, IGNITION, and LIGHTING conductors to the appropriate sources at your helm console. The wiring of the helm console is quite variable from boat to boat, so there is no way to describe precisely how to perform this. You will have to locate the appropriate wiring points in your helm console wire and connect to them.
The SENDER wire has to be connected to the engine. Often there is a pre-installed wire in the engine wiring harness which is intended to provide the tachometer signal and you simply locate this conductor and connect it to the SENDER input on the tachometer. If there is no such wire you will have to install one. At the engine you will have to deduce where to connect the SENDER based on the configuration of your motor. If you need help with making this deduction, please scan the entire electrical wiring diagram of your motor and post a high resolution image of it; I will try to help you deduce where to connect the SENDER.
It may be possible to deduce where the SENDER is to be connected by observation of the wire color codes. Generally there is consistency with these, but it is a good idea to confirm the actual function of the conductor in some other way than just its color code. Look for a legend or identifier on the engine, or some other marking that indicates the function. You could also check the voltage and signal on the conductor to confirm. As previously mentioned, the SENDER signal will be a square wave clamped at battery voltage and proportional in frequency to the engine rotational speed.
posted 05-22-2007 09:38 AM ET (US)
The marking you describe as "N461A" does not sound to me like it is a indication of function. It sounds more like a part number or date code. If the Yamaha tachometer does not have any descriptive legends you will have to rely on interpretation of the wire insulation color. Try to confirm this with some Yamaha literature.
posted 05-22-2007 06:01 PM ET (US)
Thanks, Jim, that's what I was looking for. I have a service manual for my 90HP Yamaha, so the color coding should be the same for the 30 horse.
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