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Yamaha 2 stroke 115 TRXY tach signal question and temp sensor

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Yamaha 2 stroke 115 TRXY tach signal question and temp sensor

Old 11-12-2018, 09:23 AM
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Default Yamaha 2 stroke 115 TRXY tach signal question and temp sensor

Hi All

Where does this engine get its tach signal from? Any suggestion on how to troubleshoot it?
Old 11-12-2018, 09:51 AM
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The tachometer signal comes from the CDI assembly. More than likely initiated by the lighting coil.

The green wire in the main ten pin electrical harness conveys the tachometer signal to the dash. Where it then jumpers to another green wire in a fused harness that runs to the gauges.

What specific problem are you having?
Old 11-12-2018, 09:55 AM
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Your engine gets the signal from the lighting coil. Wiring is different between the oil injected and the pre-mixed engines.



Old 11-12-2018, 09:59 AM
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Originally Posted by alloyboy View Post
The tachometer signal comes from the CDI assembly. More than likely initiated by the lighting coil.

The green wire in the main ten pin electrical harness conveys the tachometer signal to the dash. Where it then jumpers to another green wire in a fused harness that runs to the gauges.

What specific problem are you having?
Thanks for your reply! I have a Frankenstein's monster 115 that came free with a hull I purchased. It was a jungle boat serviced by a jungle mechanic.

Long story short I put a new multifunction gauge on it and I am not getting the tach signal. The gauge is a 6Y5-8350T-D0-00. the control box is a 703 side mount box with integrated key panel.

Also, I do not see the temp sensor, the seem to have been deleted. The oil injection system has also been deleted so I will be running premix.
Old 11-12-2018, 10:40 AM
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What year is the engine. You'll need a harness adapter to connect the digital gauge to an older engine. There are a few adapters depending on the year of your engine. Hopefully this page helps.



Old 11-12-2018, 10:58 AM
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as Alloyboy explained,
the tach signal gets to the gauge via a green bulleted wire which comes off the 703
(as well as ground (black) and power (yellow).

the additional harness mentioned above is not needed for the RPM indication,
but only for over-temperature, oil tank indications, and trim signal.

Running premix, you will not be needing oil tank levels.
Is there a trim sender?
Old 11-12-2018, 11:07 AM
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Originally Posted by paler View Post
Thanks for your reply! I have a Frankenstein's monster 115 that came free with a hull I purchased. It was a jungle boat serviced by a jungle mechanic.

Long story short I put a new multifunction gauge on it and I am not getting the tach signal. The gauge is a 6Y5-8350T-D0-00. the control box is a 703 side mount box with integrated key panel.

Also, I do not see the temp sensor, the seem to have been deleted. The oil injection system has also been deleted so I will be running premix.
It is a shame that the oil injection system was removed. People doing what they should not be doing. Anyway, it is what it is.

The configuration should look like that shown below, except for the remote oil tank. Does the tachometer power up when the key is turned on? If the tachometer powers up but there is no RPM indication then check all of the green wire electrical connections.

The grounds for the over temperature bar and oil status bars are conveyed via a separate wire harness. Together with the trim sender information. In the the trim and oil harness shown in the diagram. Even if the harness is not used the motor should still sound the alarm, which is incorporated within the control box. Pull the kill switch. Crank the motor. The alarm should sound.

The motor does not have a temperature sensor. It uses two thermoswitches. One in the top of each cylinder head.
Old 11-12-2018, 11:13 AM
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Originally Posted by Mud Runner View Post
What year is the engine. You'll need a harness adapter to connect the digital gauge to an older engine. There are a few adapters depending on the year of your engine. Hopefully this page helps.
OP says the motor is a 115TXRY. The Y indicates it is a 2000 model year motor.
Old 11-13-2018, 08:46 AM
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Originally Posted by Fwpratt View Post
as Alloyboy explained,
the tach signal gets to the gauge via a green bulleted wire which comes off the 703
(as well as ground (black) and power (yellow).

the additional harness mentioned above is not needed for the RPM indication,
but only for over-temperature, oil tank indications, and trim signal.

Running premix, you will not be needing oil tank levels.
Is there a trim sender?
Correct, it is wired via yellow, green and black wires from the 703 control box.
I understand that the 703 box will buzz for the overtemp, am I correct?
There is a trim sender on the engine side, not really a priority right now.
Old 11-13-2018, 08:52 AM
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Originally Posted by alloyboy View Post
It is a shame that the oil injection system was removed. People doing what they should not be doing. Anyway, it is what it is.

The configuration should look like that shown below, except for the remote oil tank. Does the tachometer power up when the key is turned on? If the tachometer powers up but there is no RPM indication then check all of the green wire electrical connections.

The grounds for the over temperature bar and oil status bars are conveyed via a separate wire harness. Together with the trim sender information. In the the trim and oil harness shown in the diagram. Even if the harness is not used the motor should still sound the alarm, which is incorporated within the control box. Pull the kill switch. Crank the motor. The alarm should sound.

The motor does not have a temperature sensor. It uses two thermoswitches. One in the top of each cylinder head.
Thank you for the diagram, I did a thorough internet search for something like this and could not find it, thanks!
I have all the parts to restore the oil injection system and gave it a shot, but the worm gear kind of jammed up twice while testing. Came to the conclusion that it was not worth rising it. Im sure it is something simple as it is a simple system, but haven´t found the fault. The bad part of premix is that you are overusing oil at lower RPM´s which is no bueno for the environment or the pocket.

The tach does power up when the key is turned to ign and the buzzer has been tested and works fine.
Old 11-13-2018, 08:53 AM
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Originally Posted by alloyboy View Post
OP says the motor is a 115TXRY. The Y indicates it is a 2000 model year motor.
Correct 2000 model year!
Old 11-13-2018, 08:54 AM
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Yes, the buzzer will sound in the event of an over temperature situation.

It would have sounded in the event of a low main oil tank situation if the system had not been butchered.
Old 11-13-2018, 08:54 AM
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Originally Posted by Mud Runner View Post
Your engine gets the signal from the lighting coil. Wiring is different between the oil injected and the pre-mixed engines.
Than you sir, good to know there is a variation.
Old 11-13-2018, 09:49 AM
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Originally Posted by paler View Post
Thank you sir, good to know there is a variation.
If you have an oil injected model, as you say that you do, why is it good to know that the premix models are wired differently?

You don't have a premix model. You have an oil injected model.

There are variations between a 115TXRY and an F115TXRD. Would it be good to know those variations? There are many.
Old 11-13-2018, 01:52 PM
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Originally Posted by alloyboy View Post
If you have an oil injected model, as you say that you do, why is it good to know that the premix models are wired differently?

You don't have a premix model. You have an oil injected model.
Because now I am wiser.

In my country the standard 115 2 stroke around that era was the premixed model. When people here talk about the 115 2 stroke they usually refer to the 115 Enduro Tuna Special that is very common on the speedboats used in commercial tuna fishing vessels.

Some of the advice I have gotten is from people who have experience with the tuna specials engines which is what the local dealer imported. They refer to mine as the US spec model, the 115 V4 very similar to the 130 (which we hardly ever see around here). Sooo it is good to know that they are inherently different, particularly due to the CDI being the one that pulses or picks up the tach signal.

I have an oil injected model converted to premix by myself, this I am certain of.
Old 11-13-2018, 02:03 PM
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Thermo switches were plugged.


Now it makes more sense.


I understand this loop is the rev limiter?


The rig


Workin´on it


Pretty girl
Old 11-15-2018, 02:26 PM
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Got the tack working!

There is a splice on the green wire on the engine harness, removed the splice and the tach picked up the signal. Still haven´t traced where the slice leads to.

Ordered 2 new thermoswitches. Also found the bullet plugs where they connect. I jumped them and the alarm buzzer sounded.

New challenge is the engine wants to run away, sounds like it is running lean. Does anyone know the typical place to start looking for air leaks?
Old 11-26-2018, 01:25 PM
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Okay, so the previous owner spliced into the engine's main wire harness to either replace or retrofit the oil injection pump. Very poorly done. I removed all the spliced wires and the tach signal is working fine.

The engine was not running away. One of the carb's levers was catching on a hose. The lever used to have the rod to connect the oil injection pump.

All issues have been cleared.
Old 01-15-2019, 12:43 PM
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Originally Posted by paler View Post



Got everything sorted out except these wires. Anyone know what they are for?
Old 01-15-2019, 03:05 PM
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Originally Posted by paler View Post
Got everything sorted out except these wires. Anyone know what they are for?
Don't know what they are for but the service manual shows them connected together. They originally were one continuous wire.

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