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240Z Tach Wiring After 123Ignition Install


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Hey Everyone,

I just replaced the stock distributor in my 11/70 240Z with a new 123Ignition unit along with a new Bosch coil.  The car now runs great, but the tachometer no longer works.  When the engine first turns on the tach jumps up a little bit, but then slams back down to 0 and stays there.  Anyone have any advice on what I screwed up?

 

Here's how things are hooked up currently (see image below for my wire numbering):

  1. [Black] The black wire going to the 123Ignition unit is connected to the coil negative
  2. [Black] There's another black mystery wire that was hooked up to the old coil negative, so I hooked it up to the same place on the new one
  3. [Red] The red wire to the 123Ignition unit is connected to the coil positive
  4. [Black/White] The green/white wire that used to connect "back" side of the resistor is now connected to coil positive
  5. [Black/White] Another mystery black/white wire that used to be connected to the old coil positive so I connected it to the same place on the new one
  6. [Green/White] This wire used to connect to the "front" side of the resistor - it's currently disconnected
  7. [Black] This wire used to connect to the little spade terminal on the old distributor, which then connected to the little capacitor hanging off the side.  There's no such terminal on the 123Ignition unit, so this is also currently disconnected.
  8. [Blue] (not shown) The ground wire to the 123Ignition is connected to the chassis

Someone in another forum had mentioned connecting wires 5 and 6 together, which I tried but no joy.

 IMG_3635.jpg

 

By the way @Captain Obvious your spring has served very well up to now - let me know if you want it back and I'll be happy to put it in the mail!

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I don't really need the spring back. Keep your distributor together in the event that you need to put it back in for some reason.

As for the problem you're having with your tach, there are a couple people here on the forum who have done the 123 ignition thing... Hopefully some of them will chime in with some help? I've not messed with that unit myself, but if you can't seem to generate any help elsewhere, I'll do what I can.

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44 minutes ago, duffymahoney said:

Your tach should just sense pulses from the coil and should be separate from the 123.

@duffymahoney Yeah, that was my hope but it doesn't seem to be sensing anything now.  I figure that wires ②, ⑤, ⑥, and ⑦ must have something to do with the tach and I just haven't hooked them up correctly.  Would you mind snapping a picture of the wires you have hooked up to your ignition coil?  What did you do with that little black wire that was hooked up to the capacitor hanging off the old distributor (mine is electrical taped along side the temperature probe wire)?

 

In better news, I went for the first real drive this morning with the new distributor and the engine feels really great.  I'm not sure if it's going to help my fuel economy, but my smiles/gallon has definitely increased.

Edited by rcv
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Yours has the current sensing tach.  I can't remember the details but people have found that fiddling with the white wire loop on the back of the tach can solve those types of problems.  I think that CO has even had  comment or two about it, but it was years ago.

Which 123 are you using. and which coil?  I think that the latest ones would pass more current than the old stock setup.  Maybe the tach is seeing too much current.

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Here's an old discussion.  The guy had the same two first initials!  Solution about post #11.  The Pertronix and 123 modules work in a similar way.

 

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17 hours ago, rcv said:

Hey Everyone,

I just replaced the stock distributor in my 11/70 240Z with a new 123Ignition unit along with a new Bosch coil.  The car now runs great, but the tachometer no longer works.  When the engine first turns on the tach jumps up a little bit, but then slams back down to 0 and stays there.  Anyone have any advice on what I screwed up?

Your Tach is expecting the stock 1.5 Ohm coil to still be there. If your new coil is a different Ohm value it will affect the Tach operation. I had the same issue here in the shop.

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Posted (edited)
1 hour ago, S30Driver said:

Maybe temporarily put the original coil back in, see what the tach does. 

Yeah, I think that's my plan. I did some more searching, and came across this great diagram by @240260280z in this thread: 

 

image.png

 

I think that basically explains it - I removed my ballast resistor when I installed the new Bosch coil which I think was the wrong move.  I'm guessing the tach is acting like a voltage divider along with the ballast resistor, and removing that resistor screws up the formula.

 I measured that Bosch coil this morning, and it reads 1.5Ohm on my meter even though it's spec'd at 1.8.  I'm just going to replace it with the old 1.5 Ohm Flamethrower coil and the ballast resistor that I had in there before.  Here's hoping I didn't fry the loop in my tach when I was playing around.

Edited by rcv
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More stuff is coming out of my brain on this topic.  It's not uncommon, I remember past discussions.  I think that in the past I suggested that a person actually divide the voltage, like you implied, purposely.  Run an extra wire around the tach circuit, parallel circuit.  Use a potentiometer to tune the current flow.  I don't know if it would work but I think that it should.

The whole point of using a current limiting ignition module is to get a stronger spark.  Using an old high resistance coil to get the tach to work defeats the purpose.  

p.s. this might be why Nissan went to a voltage spike/kickback (probably the wrong words but figurable) sensing tach for the 280Z electronic ignition instead of current sensing.

Edited by Zed Head
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47 minutes ago, Zed Head said:

Run an extra wire around the tach circuit, parallel circuit.  Use a potentiometer to tune the current flow

Yeah that's a good idea. You might need to put a very small resistor in parallel with the potentiometer, otherwise the current through the pot will be super low and subject to whatever the impedance is in just the wiring.  The goal would be to make the current flowing through the pot+tach the same as it used to be, but to also get some extra juice by pulling in extra current through the low-ohm resistor that's in parallel.  I'm not sure when I'll have time to source the parts and try this, but it sounds like good experiment.

tachometer.jpg

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I’m running 123/Tune+ with a non-standard coil and no ballast resistor. This is on a ‘73 240Z. The tach works & exactly matches the 123App. I just jumpered over the ballast resistor (in effect). Actually I put both wires on one side of the ballast resistor as that was easy. I do not know if my tach is different from other earlier ones.  I think it’s the “current loop” type.

Richard (alienpoker on YouTube)

Edited by Firepower
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1 hour ago, Firepower said:

I just jumpered over the ballast resistor (in effect)

Thanks Richard - I believe I tried that, but had no luck.  I'll give it a shot later and see if I can figure out what I screwed up. When you say you jumpered both wires, you mean the Black/White wire, and the Green/White wire right?

Also, thanks for the "240Z 123 Ignition Tune+ Install" video you did you Youtube, it was my main reference when I installed mine and it was a huge help.

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No problem.  I really liked the tuning capabilities of the 123ignition dizzy for the L6.  You can have a tame tune for when you feel calm and want decent milage and a more “spirited tune” that you load for carving canyons or sporting around.

You are correct, from memory I have the green/wht, black/white and red wire to the 123/tune+ all on one side of the ballast resistor. Nothing on the other side.  The other black/wht wire goes to the coil.  So yes, I connected Green/wht, one Black/wht and the Red together. Everything works as it should. 
Hope this helps.spacer.png

 

FC2547CF-DA66-4277-8FC1-16DB6EC63ECD.jpeg

Edited by Firepower
Added picture of dizzy wiring.
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On 3/2/2021 at 1:34 PM, Firepower said:

I have the green/wht, black/white and red wire to the 123/tune+ all on one side of the ballast resistor. Nothing on the other side.  The other black/wht wire goes to the coil.  So yes, I connected Green/wht, one Black/wht and the Red together. Everything works as it should.

Wahoo it works! Thanks for the help @Firepower  

For anyone else who stumbles n this thread, here’s how I wired it up. I made a “Y” connector to connect the following wires:

- Green/White

- Red wire that goes to the distributor

- Black/White wire that gets 12V when your key is switched to “on”.

 

The other black/white wire (which does not read 12V when the key is in the “on” position) goes to the positive terminal of the coil.

 

0E416A1C-686A-45BB-A78F-6133BD52B59D.jpeg

 

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  • 2 months later...

Hey Guy´s.

 

I´ve the exact same problem/behavior like the thread starter but with a 280z. So I should have the tach that works right away with the 123 dizzy, but it doesn´t.

Mine is MJ 78 so it comes with no ballast resistor and with transistor ignition unit from factory.

 

During the restoration I changed the stock coil to a red Bosch with no resistor and removed the stock ignition unit completely.

The 123 is hocked up iaw instructions, red to coil+, black to coil - and blue to ground.

Elec. Fuel injection is removed completely as well -> exchanged with Webers.

 

So the tach gets its sensing cable from the minus side of the coil via a resistor. Nothing else is connected in line with it anymore.

I´ve measured the stock resistor, it has a value which I can´t confirm because I can´t find the oem value anywhere to check it to, but at least it has continuity. 

 

At first I thought of a ground problem of the tach itself as I just had the dashboard hanging lose during testing phase but now that everything is bolted down and still shows a jumping needle and when you push the throttle it goes back to 0. I probed the tach and its ground connections/metal strap and also tach to dash - all grounded perfectly.

 

Coil + has nothing but the black/white wire and no capacitor as 123 says its build in anyway.

Coil - has the 123 dizzy black, the tach sense wire and my fuel safety relay sense wire connected.

 

 

If I remember right my tach also doesn´t have that magnetic field loop mentioned in the other thread. But maybe a ferromagnetic ring thingy around the sense wire like you have on some electronic devices might help?

 

 

Any ideas?

Thanks in advance.

 

To be honest I´ve no idea where to start. Probably jumping the stock resistor in the sensing line and see what happens or run a new wire directly from the coil to the tach. Maybe a connector issue ?!

stock wiring 280z.PNG

tach 280z.jpg

Edited by PrincePaul
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29 minutes ago, SteveJ said:

The resistor value is 2.2kOhms.

Thanks I’ll check.

I also found in some other thread that someone installed a capacitor like on the generator or coil in the sense line to smooths out the signal or a diode.

There is easy access to the resistor I might try those but now that the dash is in its really hard to get to the back side of the tach. Especially cause the dash has a cover on it…

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8 hours ago, PrincePaul said:

Coil + has nothing but the black/white wire and no capacitor as 123 says its build in anyway.

Coil - has the 123 dizzy black, the tach sense wire and my fuel safety relay sense wire connected.

By "tach sense" wire you mean the blue wire that heads back past the ignition module, right?

What is this "fuel safety relay", and how is it connected/wired?  That would be new to the system.  The tachometer seems sensitive to the signal on that wire.  You could disconnect it for a test and see what happens.

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46 minutes ago, Zed Head said:

By "tach sense" wire you mean the blue wire that heads back past the ignition module, right?

What is this "fuel safety relay", and how is it connected/wired?  That would be new to the system.  The tachometer seems sensitive to the signal on that wire.  You could disconnect it for a test and see what happens.

Yes the blue wire. That one basically goes only from coil minus to tach, nothing else.

 

that’s the diagram for the pump.

It basically shuts the pump off if you’ve an accident.

D322CA8D-74BB-4FF4-AA05-D1B4B8CA363E.jpeg

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Is it an inertia switch?  It looks like it supplies power to the coil also.

Have you disconnected/unplugged the factory ignition module?  While you're down there you can also test continuity back to the coil negative.  It's a branched circuit, one to the ignition module, one to the tachometer, one to the ECU.

The condenser/capacitor on the blue wire is easy to setup.  That's what worked on mine, with a GM HEI module.  Any condenser from an alternator will work.  The wire to the capacitor goes the coil negative, the capacitor can be mounted on the ground point on the manifold, nearby.  It's a cheap quick test if you have one laying around.  Won't hurt anything.

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No it’s a relay that powers the pump when ignition is sensed via the coil negativ. It does not supply power to the coil. It goes to coil pickup 1 which is the negativ side.

 

yes the factory unit it all gone also factory ecu. Yeah I’ve the old one from the positiv side of the coil, which I could easily hook up to the negativ side. But I’ll also try removing the fuel safety relay wire just in case. 
 

so 4 possible solutions right now:

1. wire problem, but as it senses something I guess not the case maybe still ground problem. Should be easily checked by direct wiring or probing

2. negative effect from the fuel safety circuit

3. interference where a condenser might help

4. resistor value wrong

 

 

i might also try the factory coil which was installed on the car - maybe it requires a different ohm value. But as it’s on the negativ side i don’t know why the Tacho would be affected by that.

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1 hour ago, PrincePaul said:

No it’s a relay that powers the pump when ignition is sensed via the coil negativ. It does not supply power to the coil. It goes to coil pickup 1 which is the negativ side.

Couldn't really tell from that diagram which is positive and which is negative.  Why would negative or positive matter if it's just sensing power?  (Edit - actually I don't really understand how that device works.  Maybe it's "sensing" sparks?  Current flow?  Whatever it is, the positive side might work the same.  @SteveJ  @Captain Obvious )

If you have another load on the negative terminal of the coil that could screw up your tach signal.  I'd disconnect that before you get too far along and see if it starts working.  I don't know if the condenser will help you with that scheme.

If it fixes the tach problem try using the positive side of the coil for the power signal.  Edit - actually don't try this.  It might be a direct short, depending on how the device works.

Edited by Zed Head
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