Tacho Wiring

thrash · Post by **thrash** » Sun Jul 24, 2011 2:34 pm

The electronically challenged needs some assistance please!

Which wire at the back of instrument cluster is for the tacho driver? Thanks in advance everyone!

Xentro · Post by **Xentro** » Tue Jul 26, 2011 6:35 am

See the screw with IG (-)
Follow that trace and you've got yourself the tacho wire.

If you want to use your stock tacho on a aftermarket ecu you may have to modify the tacho itself.

thrash · Post by **thrash** » Tue Jul 26, 2011 12:36 pm

Thanks Xentro!

Does the standard tacho accept a sine wave or square wave?

DrDeath · Post by **DrDeath** » Tue Jul 26, 2011 2:53 pm

I had to use a MSD Tacho adaptor with my EMS stinger to get it to work.

OLD FART · Post by **OLD FART** » Tue Jul 26, 2011 5:28 pm

^^^^ same here with my Haltec E6X

avandull · Post by **avandull** » Tue Jul 26, 2011 9:20 pm

I dismantled the tacko itself and changed a resistor value so that it would work with a 12 volt square wave input.

You will need a soldering iron.

Let me know if you are interested.

enthuzed · Post by **enthuzed** » Wed Jul 27, 2011 8:46 pm

For Sale: 1 tacho repairing soldering iron.

Wasn't there a post of that mod a while back?

thrash · Post by **thrash** » Thu Jul 28, 2011 1:48 pm

I have a soldering iron.. somewhere.. lol

Back when I was doing my degree, electronics was a major part, so I had some decent equipment, but no interest in the subject. I also didn't have a car then. lol

time to find all my equipment and actually bother learning the stuff!

Thanks for your help everyone! My car has the VR4 tacho adaptor thingo, near the coils. I just wanted to know where I need to wire it into. Should have figured it was the negative ignition point, considering that's what the factory wiring diagram says lol!

Post by **TOMSUN** » Fri Jul 29, 2011 9:09 pm

I also had to put a "pull up resistor" in line to make it work with my EMS 8860 and twin coil ignitor. Cost 10c.

http://forums.austarion.com/viewtopic.p ... l+resistor

thrash · Post by **thrash** » Sun Jan 27, 2013 10:15 pm

digging this up again.

What kind of waveform does the starion tacho need to work?

put together a jaycar waveform generator modded to output between 10hz and 2700hz instead of their audio range of 120hz to 20khz, hooked it up to the tacho, but got nothing - either i'm not connecting it properly, or the tacho simply does not like a 5v ac square wave? My next guess is that it requires 12v, so i might put together a basic amplifier and try, but thought i'd ask first

the 3 connectors on the tacho are marked IGN+, E and IGN-
I am assuming E is just ground, but when i connect the waveform generator to ign+ and ign-, nothing happens.. any ideas?

ProZac · Post by **ProZac** » Mon Jan 28, 2013 6:19 am

The factory tacho accepts the big inductive kickback spike generated by the coil, its a 300+V very short duration pulse. This is pretty much the way all older style tachos work

You can make it work with a 5v square wave by simply putting a jumper across the first resistor inline with the circuit.

Pull the tacho out, and look at the PCB. the 'IG' terminal on the tacho will lead directly to a resistor. I can't remember what value it is, but I think it was a pretty high wattage one, so physically quite large. Simple solder a wire to either end of the resistor, jumping across it, and effectively cancelling it out. Doing it this way makes the modification easy to reverse :).

That resistor removes alot of the energy from the big pulse, allowing it to safely interface to the tacho's internal circuitry. As your now sending it a low energy pulse, it's no longer needed.

I've got one sitting on the workbench infront of me working off a 5v 50% duty cycle square wave, works perfectly :). This modification works on a heap of tacho's from the 80's and 90's that took a signal from the coil negitave post. We make the modification a lot to get them to work with the 5v LINK ecu tach output.

[edit for clarity] All references to 5V squarewaves in this post should say 12V, was a might confuddled when writing it, hah [/edit]

ProZac · Post by **ProZac** » Mon Jan 28, 2013 6:21 am

As to the IGN+, IGN- and G, I'm not sure what's going on there, as I have 'B', 'E', and 'S' on mine, as in Battery (+12V), Earth, and Signal, hooked up to mine. Can you post a picture?

ProZac · Post by **ProZac** » Mon Jan 28, 2013 7:25 am

Whoops, I meant 12v square wave, I'm driving it through a level shifter up to 12v.

Might still work with a 5v signal, but I dont know how much current it draws, and I dont want the fry the ouput port of the microprocessor it's attached to, so not keen to hook it directly to it, heh.

thrash · Post by **thrash** » Mon Jan 28, 2013 9:38 am

the big resister is red purple orange gold - 27k

I can't get it to work :(

I used an aligator clip to connect to the other side of the resister - the resistor only connects the IG- to the rest of the tacho circuit

What should I connect where? I tried a few different combos, but nothing worked. One of the combos made the tacho jump to the first bar for a fraction of a second (not the 1000rpm bar, the tiny bar just above the needle resting point), but then nothing after that, even though the generator is still producing frequency

pics:

ProZac · Post by **ProZac** » Mon Jan 28, 2013 2:28 pm

Crap, I'm home now and it's no longer infront of me.. But on the PCB itself it'll have three letters, I think they are B E and S?

Austarion

Tacho Wiring

Tacho Wiring

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