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Thread: how to wire a pertronix up when you have a 3 kohm coil on a 71 240Z.

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    Supporting Member Zedyone_kenobi's Avatar
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    Default how to wire a pertronix up when you have a 3 kohm coil on a 71 240Z.

    I spent some time last night with a wiring diagram, a soldering iron, and a beer looking at my ignition wiring to see if anything is wired funky that could be messing with my voltage going to my pertronix and coil. I discovered a few neat things.

    First the way the coil gets its power. I think this is cool (although it is old school to most of you I am sure). In the stock configuration when you turn the key to the last position right before you start, the coil gets its voltage after it runs through the ballast resistor. A stepped down voltage if you will to protect the points I would imagine.

    Now when you turn the key, the ignition sends 12 V straight to the starter AND to the coil and the extra voltage is used to help start the engine with a hotter spark. I really did not know this. But after staring at lines on a wiring diagram all night (I really hate dealing with wiring BTW) this hit me.

    So I was laying in bed at night and I thought that the way it was wired my pertronix is getting 13+ volts during engine run. I thought that the pertronix had to have 3ohms in place to step down the voltage.

    Here is a description of how I have mine and how I understand it. Keep in mind I have a 3kohm coil.

    Click image for larger version. 

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    First check this for sanity, and if okay, hope it helps others.
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    Last edited by Zedyone_kenobi; 03-22-2012 at 07:24 AM.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Registered User MotoManMike's Avatar
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    Appears to me the way its wired, the ballast resistor isn't doing anything. If I remember correctly though you had to use the higher ohm coil to even use the pertronix and i used the ballast resistor on both my cars. I will send pics when I get home tomorrow if you need. Mine both run great using the pertronix/flamethrower. I have converted both my 73's. My ignition is as stable as I can get it with that set up and tuning is much easier. The tach jumps at high RPMs but i have a pretty good gauge by ear so no worries. It is interesting though and never occured to me they let full battery voltage to it originally when starting. They were very thorough when designing these cars indeed even almost 40 years ago, its pretty amazing.

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    Supporting Member Zedyone_kenobi's Avatar
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    Well if you use a 3 kohm coil you no longer need the ballast resistor with a pertronix. At least that is the common factoid talked about around here. You are right, my ballast is not doing anything. But I leave it on as a convenient way to connect wires.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Administrator bpilati's Avatar
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    I thought the ballast resistor needed to remain for the tach.
    Bryan Pilati
    1971 Datsun 240Z (8/71; 920 paint)
    IZCC #583; TZCC #16; CZC #110
    I'm never serious unless I should be.

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    Semi-retired admin Arne's Avatar
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    Quote Originally Posted by bpilati View Post
    I thought the ballast resistor needed to remain for the tach.
    A 3Ω coil is essentially the same electrically as a 1.5Ω coil with a 1.5Ω resistor. I ran my '71 both ways at various times, tach worked fine either way. After my 3Ω Pertronix coil died, I went with a 1.5Ω Crane PS20 which came with its own matching resistor.
    Arne - Former owner, HLS30-37705, 7/71, 905 Red
    Car blogs - 240Z - Porsche 911

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    Supporting Member Zedyone_kenobi's Avatar
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    Lets see.

    If I were stock, I could not sent the full 13V to the points. At least for not very long. So I would have had to run it differently.

    For instance. I think I would have to connect the black/white (3) wire that gets battery power with the key in the run position to one side of the 1.5 kOhm ballast resistor.

    Then, since on a 71 the wire that gives the coil its power (green/white) has to go through the tach first and then back to the coil and dizzy. I would have hooked up the green/white wire to the opposite end of the unbridged ballast resistor (thus dropping the voltage going through the tach and back to the coil through the black/white wire (4). This way the tach would see about 10 volts (well less than 13V anyway) , which means the coil would only get about 10 volts, resulting in a weaker spark that would not prematurely destroy the points. If you ran a 3kOhm coil you could bypass the ballast resistor altogether, but your tach will see the full voltage during engine run and your coil would receive more input voltage.



    Actually, I am not sure how the coils resistance matters at all. The way it is wired.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Registered User beermanpete's Avatar
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    Quote Originally Posted by bpilati View Post
    I thought the ballast resistor needed to remain for the tach.
    No. The tach does not care about the circuit resistance. The ballast is mainly to prevent the coil from overheating when the engine is running at low speed.

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    Thank you this may help me get my Zelda running I didn't have any good wiring diagrams.

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    Zedyone, thanks for this information. I will be putting in a pertronix and a 3 ohm coil, but I wasn't planning on reinstalling the ballast resistor (the one that was on the car is shot). I was hoping that you could revise your drawing to show how I would be doing this without the resistor. Thanks for any help you could give.

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    Registered User grannyknot's Avatar
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    Quote Originally Posted by 240tom View Post
    Zedyone, thanks for this information. I will be putting in a pertronix and a 3 ohm coil, but I wasn't planning on reinstalling the ballast resistor (the one that was on the car is shot). I was hoping that you could revise your drawing to show how I would be doing this without the resistor. Thanks for any help you could give.
    If you are going to install a Pertronx ignition module just be sure that you don't have the key turned to ON for extended periods without starting the engine.
    There are a few threads on this in the archives and I burnt out one this winter while I was trouble shooting an electrical problem.
    1970 240Z HLS30 01955 March/70

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    Although I don't own a Pertronix set-up & know virtually nothing about it, I've repeatedly read about this little problem of leaving the key on & and frying it, I'll leave the question of why anyone would sell or buy this product, to anyone who would like to educate me. The thing I'm curious about is, does anyone know how long you can safely leave the key on? Everyone writing about the problem seems to have a vague idea of the time frame. I'd be afraid to buy one for that reason alone. I really am curious about the positives this system offers because Pertronix was one of the options for an upgrade.

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    I never had a reason to have the key on and not have the engine running to be honest. I gave it relatively little thought and never had a pertronix failure.
    I think it is just a kind word of caution. Be aware, do not jam with the radio on and the one speaker blaring for too long with the key in the on position.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    I don't think that Pertronix even considers the Z cars as a market anymore. You have to search for an Ignitor by distributor number and none of the numbers I've seen listed for 240Z's show up. I checked the two FSM's that are available on the web.

    Also, if you open any of the instructions for the Ignitor I kits you'll see that one of the first statements shown is about leaving the key on. The Ignitor II is more like the stock 280Z module or a GM HEI module in that it has circuitry to prevent overheating, probably some sort of timer that cuts current if there's no action within a certain time. I'm guessing from previous reading. Plus they took out the warning about leaving the key on. The II also has "dwell" (current) control like the GM HEI and the stock 280Z modules. Plus you don't have to worry about resistors or ballast, just get a low resistance coil. If I was going to use an Ignitor, I would find a II that works. How you find one though, is the dilemma, if it exists. The Ignitor I is old technology but I guess place like MSA will keep selling as long as people keep buying.

    JEGS seems to think that this Ignitor II fits a Z distributor although the Pertronix site doesn't. It's a problem.

    Pertronix 91761 Pertronix Ignitor II Kits - Free Shipping on All Orders @ JEGS

    Ignition Products
    1976 280Z, with some minor modifications

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