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Old 01 April 2014, 09:01   #1
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Tacho wiring help

After I managed to fry my last tachometer by disconnecting the battery whilst the engine was running I have picked up a vintage yamaha one from eBay.

Problem is, I have no idea on the wiring. The last one had:

- signal
- ground
- positive

But I can't work this one out??? Does anyone recognise this model or remember which terminal is which?

There are some numbers on the plastic.

The one on the far lefthand side says 12 (maybe switched 12v goes here)

It is joined to B? (Bulb)?

Middle one is 4?

And righthand one is G (ground?)

No idea on the top two!!!
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Old 01 April 2014, 09:02   #2
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Here is the tacho
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Old 01 April 2014, 16:44   #3
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The pulse goes onto the middle of the three. Use the link for either a 4 pole or 12 pole alt it must bridge either or. The other terminal bottom right b? Is for your neg/ ground/ earth. Try fitting it into your dash first as these are 6mm smaller in diameter than the later ones and will possibly fall straight through the hole.
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Old 02 April 2014, 00:56   #4
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Thanks Davie, that is not a configuration I would have guessed!

Where does the positive go? Also just measured it and I think you are right it's gonna fall straight through. Agggghhhh!

Does anyone know if a yamaha 55b would go on a 4 or 12 setting?

Might just sell this one and buy a faria one
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Old 02 April 2014, 16:24   #5
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Davie you were right, it does just fall through the hole!!!

Still can't get my head round the wiring though. The top two leads are the light, it pulls out so is independent to the rest of the tachometer.

What you said about moving the bridge between the contacts makes sence, from what I can gather older yammies were either 4 pole or 12 (larger engines) but where does the switched + go?

Is it possible the tachometer will work without + input.

I have spent all day at work trying to research it and am completely stumped!
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Old 02 April 2014, 16:52   #6
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Try it. The yellow 12volt feed plugged into the blue which powers the backlight. Join the blacks together. Btw if you wrap insulating tape round the gauge 10 times at the lip ( glass end ) it will by magic not fall through the hole, that assuming it has been drilled at 83mm.

Tell you what pole setting you require for 55 tomorrow.
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Old 02 April 2014, 18:33   #7
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Yam 55 is 4 pole, however some of these tacho's were for 6 and 12 and others for 4 and 12. Both were identical. I bought the wrong one for my RIB. I never knew there were different ones but looking back through some old manuals there were two different part numbers.

You only need the black and green wire to operate these. The yellow is not required, but using it for the bulb may be a good idea.
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Old 03 April 2014, 03:25   #8
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Davie and Rib-Teccie, many thanks I am always astounded by the wealth of knowledge on here I spent hours trawling the internet yesterday and didn't even come close!

I will get down to the boat later and plug it in as outlined above and let you know how it goes...

Thanks again, Simon
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Old 03 April 2014, 08:33   #9
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Looking at the photo's if does look like the correct one, mine has 6 and 12 moulded into the plastic. If it is the wrong one it will only register about 4000rpm flat out, even though you know the engine is putting out more than that.

If you decide to go with a faria to match your dash, I would be interested if you are selling and it is the correct one.
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Old 03 April 2014, 15:21   #10
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Well it works! So a massive Thankyou to you both

Weirdly the wiring was the reverse to what I had thought.


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Excuse the purple, that is borrowed from the mercury gauge and links to the green!

Anyway as Davie pointed out it does fall through the hole, I have wrapped it in black tape but whoever cut the original hole made a bit of a hash of it so I am working on plan b, if that doesn't come off then the gauge could be for sale.

Thanks again though, Simon
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