tach question for a 1998 nissan 25c3

[warrenhemby]

i have a remote operated 25c3. the directions on the nissan tach tach tell me to plug into the remote gearbox via harness (3r0725371m) but mine has no pigtails or extra wires. Paul stated in an earlier post about a harness for a tiller operated motor (361725390m). does this harness simply allow for a tach to be plugged in and mounted where ever you need it. i will need about 13 feet of harness. Just didnt want to have to make one and it look like crap. Thanks in advance.

 

[pvanv]

Re: tach question for a 1998 nissan 25c3

The 361725390M, LEAD WIRE TACH 20', $44.40, is for tiller models-if for EP (remote motors), use 3R0725371M, LEAD WIRE, METER, $56.13

Also remember to set the rotary switch on the back of the tach correctly, in your case, 4-pole:

Tachometer pole settings:

TLDI: All models: 4-pole setting

4-strokes: 2hp to 9.8hp: 6 pole setting
9.9hp to 30hp: 12 pole setting

2-Strokes: up to 40C: 4 pole setting
40D~90A: 6 pole setting
115~140: 12 pole setting

 

[warrenhemby]

Re: tach question for a 1998 nissan 25c3

Thanks paul. My remote has no extra wire except for key and choke. Nissan answered me with I need to use tiller harness and an adapter 3p0726790m cause mine model is missing an pulser and it has a 2 wire exciter....sound right to you??..again thanksgivings for your help

 

[pvanv]

Re: tach question for a 1998 nissan 25c3

Sounds exactly right. You will want 3P0726790M TACHOMETER SENDING UNIT $22.68

 

[Sea Rider]

Re: tach question for a 1998 nissan 25c3

Paul,

Bought a TSU by mistake thinking it was a tacho, but no, it’s a black plastic case with 1 male, 1 female wires. Is shown on the parts manuel for 2 strokes 18-25-30 models, was wondering if it will work ok on a 40C. Supposedly will need to use 3AC726400M TACHOMETER - BLACK (FTC8138) As B7725301 is NLA, is this right ?

One issue not clear, is it possible to use this combo with rope or electrical start engines as the black case seems a kind of induction unit ? If so, how far from engine can the tacho be intalled if using a console ?

Happy Boating

 

[pvanv]

Re: tach question for a 1998 nissan 25c3

The 40C used 3B7725302M, but that tach is NO LONGER AVAILABLE. USE 3AC726400M (BLACK) OR 3AD726400M (WHITE). If your notor is rope start (and for some strange reason does not have an alternator), you will also need the TSU. If your motor is stock, and has the alternator, you're fine without the TSU.

 

[HaMm3r]

Re: tach question for a 1998 nissan 25c3

Sounds exactly right. You will want 3P0726790M TACHOMETER SENDING UNIT $22.68

I know this is an older thread, but thought it would be better to reference the preexisting information than re-explain everything. I also was told that I needed a 3P0726790M Tach Sending Unit, but it doesn't appear to have helped and I can't for the life of me find any documentation or diagrams that show how to hook it up. I can only assume that it just plugs in-line into the white wire from under the flywheel, since the TSU leads are male/female white. Would anyone know if this is correct?

Thanks in advance!

 

[pvanv]

Re: tach question for a 1998 nissan 25c3

You really should start a new thread, as this one is 3 years old.

The wiring diagram for the original 25C3 is in the owner's manual at http://www.tohatsu.com/tech_info/own_man_pdfs/Toh25C3_30A4_40C.pdf

The tach sender wires are white and yellow. The tach sender is needed to accommodate a new-style Tohatsu/Nissan tachometer, if that is what you have, because the 25C3 does not have both exciter and trigger coils. If you have an aftermarket or off-brand tach, it may not operate correctly.

If that is your setup, I can fax or email you a sender wiring diagram.

 

[HaMm3r]

Re: tach question for a 1998 nissan 25c3

Thanks Paul,
I was hoping you'd respond since you seem to be the man with the answers here. I've already checked those wiring diagrams. I have that service manual and I don't see the TSU listed on any of them, at least not in a way that I can decipher. I do have an aftermarket tach made by Teleflex and I'd rather not change because it matches the rest of my console gauges. That's why I ordered the sending unit.

Also, not to be argumentative, but the tach sender wires are white and white, not yellow (pictured below). That's what led me to post the question here about how it's connected. Any suggestions beyond replacing the gauge?

 

[pvanv]

Re: tach question for a 1998 nissan 25c3

The sender goes in series in the white wire of the tach signal wire. There is also a yellow tach "ground" wire -- hence we refer to the tach wires as being yellow and white. (BTW, Your manual does not take into account the new-style tach, which came out after the manual was printed.)

Remember to set the correct number of poles on the tach. If your tach is not an alternator tach, but rather an ignition tach, all bets are off, and you may need to (likely will have to) get the correct tach. See the attached diagrams:

 

[HaMm3r]

Re: tach question for a 1998 nissan 25c3

Those are a big help Paul. Never saw those before. Thank you!

Let me ask you one more thing, keeping in mind that I'm working with an aftermarket tach and I understand there are no guarantees. The yellow wire, which you referred to as a ground, should I connect that to the ground terminal on the gauge? I've been trying to get it working with just the white wire connected to the "send" terminal. Currently, the tach is connected to a common ground shared by all the electronics on the boat, including the outboard. I don't want to damage anything by tying the yellow into that common ground if it's not supposed to be.

Thanks again!

 

[pvanv]

Re: tach question for a 1998 nissan 25c3

In a Tohatsu tach, I typically use the yellow as Tach Signal Ground, because it's in the tach harness and handy... But you should be OK using regular battery ground. I've done it both ways. Ground is ground. But the yellow wire is a light gauge duty conductor, and is not intended to be the ground for all the electronics (and instrument lights) on the boat. The 12v that powers the tach should be switched off when the motor is off, to keep from draining the battery. There should be a pole selector switch on the tach, which must match the number of poles in the motor's alternator. If not, you may have an ignition tach... in that case, you will likely need to get a correct (Tohatsu) tachometer.

 

[HaMm3r]

Re: tach question for a 1998 nissan 25c3

Ok, appreciate the info once again. My tach does have the pole selector dial, so what I'm going to try is to connect the white from the TSU to the tach's "send" terminal and then connecting the yellow from the alternator to the "ground" terminal on the tach. I'll post the results.

As for the system ground, yeah I wouldn't use that wire for all the electronics. I've got +/- distribution blocks in the console that everything wires into and all the gauges are on a switch in the panel, so I can turn them off when not in use.

 

[HaMm3r]

Re: tach question for a 1998 nissan 25c3

Well, I promised I'd post the results of my Teleflex tach and TSU testing, and I found that connecting the yellow wire from the alternator to ground does indeed allow the tach to work. However, that is true only up to about 2000 RPM. Beyond that, the tach begins to read approximately double what it should. I have a Tiny Tach which is very accurate that I used for verification, plus you can tell just by the sound of the motor that it wasn't running at the displayed RPMs. I did try changing the pole selector dial, but then it's wrong right from idle. I also hooked it up without the TSU in line, just to see if it made a difference and it really didn't. The only thing the TSU seemed to improve was that it eliminated a tiny bit of needle fluctuation with the tach reading. Then just to be sure there wasn't something else in the electrical system causing interference, I disconnected all other external electrical and ran a separate temporary circuit with only the tach, tsu and battery on it. So, it seems to me that I'm out of options for using my Teleflex tach with this outboard's factory tach leads. Any suggestions?

 

[pvanv]

Re: tach question for a 1998 nissan 25c3

Are you set to 4 poles on the tach?
Did the tiny tach read correctly?
If so, you need the correct Tohatsu tachometer.

 

[HaMm3r]

Re: tach question for a 1998 nissan 25c3

Yes on the poles. I started out with the 4 pole setting, then switched to 2, then 3. Only the 4 pole setting was accurate below 2k. The Tiny Tach did read correctly through the entire range and always has. I've had it on this motor for a few weeks and have used it on other motors previously, so I know it's very reliable.

Interestingly enough, I have an aftermarket GMR tach signal sensor that I've used with past outboards before. I decided to hook that up to this motor and wire the Teleflex tach to it instead of the factory tach leads. So far, it seems to have solved my problem. Of course, I'm only willing to wind the engine up to about 3k on the muffs, so I can't yet confirm that it remains accurate all the way up to 6k, but I'll try to water test it today or tomorrow to verify. With any luck, the GMR will let me keep my matching Teleflex gauge.

 

[HaMm3r]

Re: tach question for a 1998 nissan 25c3

Ok, I think I've got the aftermarket tach problem solved. First though, the GMR tach signal sensor I mentioned earlier did not work at higher RPMs. Once I got over about 2500, the readings began to fade and eventually it would just hover around 2k. I think it became overwhelmed by electrical interference. So, I went back to the Tohatsu 3P0726790M Tach Sending Unit and reinstalled it with the yellow wire connected to the engine ground and the white going thru the TSU to the "send" post on the Teleflex tach. At first, my results were the same as before, with higher RPM readings being way off. So this time I tried turning the pole dial up instead of down, first to the 5 pole setting and then to 6 pole. On the 6 pole setting, the tach readings were nearly perfect thru the entire range and closely matched what the Tiny Tach was showing. So basically it's fixed and I get to keep my matching console gauge scheme intact!

Any thoughts on why the 6 pole setting works, when everything I've read says that tachometers on this motor should be set to 4?