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SD25/27 Tacho signal, where from?

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Mal B

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I'd like to get the original tacho working with the VN V6, but after hours of fruitless searching have been unable to find where the signal came from, on an SD25.
Bought a Haynes manual, thinking the wiring diagrams would help, but it only covers the petrol motors.
Any info will be greatly appreciated.
Mal
 

tweak'e

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usually comes from the injection pump with most of those diesels of that era.
you will need a converter to get the vn signal to work on the original tacho.
 

Mal B

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usually comes from the injection pump with most of those diesels of that era.
you will need a converter to get the vn signal to work on the original tacho.
Oh well, chuck that idea in the too hard basket, and start looking for an analogue clock to fill in the hole. Gotta have something moving there, otherwise it'd drive me to distraction.
Thanks ATD Mate.
 

izzibri@gmail.com

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i used a tacko off a 93 nissan which worked off the alternator wire.. since my alt didnt have the terminal i pulled it a appart and solded a wire (look up how to wire your tacko into an alternator )
 

Mal B

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actually the vintage of your car may have it wired to altenator
I've actually watched that video, and I've had a long hard look at my alternator to see if it's got a "W" terminal, but I'll have to take the alternator off to be sure, because of all the pipes, tubing, wiring and rocker cover in the way. At least I'm sure, if there is one, there's no wire attached.
I'd love to be able to find a wiring diagram for the SD25, to see where the pick up comes from, there's heaps about for the Zs, but they all come from the coil.
Did you just change the tacho, or swap the whole cluster, and do you remember which wire was the signal wire going to the tacho?
I may have to do some experimentation, it's not working now, so what's the worst I can do😁.

Cheers
Mal
 

Mal B

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I've been thinking, again 🤬. If the tacho got it's signal from the injector pump, wouldn't that have to have been from a "Hall" or proximity type sensor?
And if so, would it not be possible to set up something similar on the any one of the pulleys? Just have to find the right rate of spin, or number of magnets.
Tacho is a four wire job, with one wire ignition +, one earth -, haven't been able to figure out the other two, yet.
 

izzibri@gmail.com

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I've actually watched that video, and I've had a long hard look at my alternator to see if it's got a "W" terminal, but I'll have to take the alternator off to be sure, because of all the pipes, tubing, wiring and rocker cover in the way. At least I'm sure, if there is one, there's no wire attached.
I'd love to be able to find a wiring diagram for the SD25, to see where the pick up comes from, there's heaps about for the Zs, but they all come from the coil.
Did you just change the tacho, or swap the whole cluster, and do you remember which wire was the signal wire going to the tacho?
I may have to do some experimentation, it's not working now, so what's the worst I can do😁.

Cheers
Mal
use a mirror to see, i think its an after market fit , either injector line or alternator. if its alternator look for a wire thats been drilled or hanging out of back housing.
 

izzibri@gmail.com

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use a mirror to see, i think its an after market fit , either injector line or alternator. if its alternator look for a wire thats been drilled or hanging out of back housing.
some early petrlol engines had coil connections i think about 8volts supply....alternator is 12v+ dont know if you can use same tacko
 

tweak'e

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I've been thinking, again 🤬. If the tacho got it's signal from the injector pump, wouldn't that have to have been from a "Hall" or proximity type sensor?
And if so, would it not be possible to set up something similar on the any one of the pulleys? Just have to find the right rate of spin, or number of magnets.
Tacho is a four wire job, with one wire ignition +, one earth -, haven't been able to figure out the other two, yet.
you could do it that way. bit of a pita job.
the more common way is to just use a converter box. it simply changes the frequency output to match what the gauge uses.
however probably the more common way when doing petrol conversions is to go get the dash out of the petrol version. that way it can actually display the whole rpm range.
 

Mal B

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you could do it that way. bit of a pita job.
the more common way is to just use a converter box. it simply changes the frequency output to match what the gauge uses.
however probably the more common way when doing petrol conversions is to go get the dash out of the petrol version. that way it can actually display the whole rpm range.
Didn't even think about differences between petrol and diesel, just dashed out and checked, 4,300 rev limit.
How close would a cluster from a VG30 Pathfinder be to plug and play, with a re-wire of the tacho? One on eBay with similar ks on the clock, and nearly half a tank of fuel, in the gauge🙂.
 

tweak'e

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Didn't even think about differences between petrol and diesel, just dashed out and checked, 4,300 rev limit.
How close would a cluster from a VG30 Pathfinder be to plug and play, with a re-wire of the tacho? One on eBay with similar ks on the clock, and nearly half a tank of fuel, in the gauge🙂.
i don't have wiring diagrams of d21 to be able to check.
 

tweak'e

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Seems to be a dearth of diagrams on the net, which, in my case, could be a good thing, coz they do my head in🥴
i have the same problem with my other 4x4. digital manuals didn't really exist back then. i have some blurry pics of the paper manuals.
 

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