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Points get resister wire less than 12v and HEI get full 12v

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  • Points get resister wire less than 12v and HEI get full 12v

    Yeah, maybe. Or not, as the case may be.

    Working on sons' '72 Nova. Its very original, 250 straight 6 powerglide, manual drum brakes and manual steering with a green color matched rubber floor mat.

    Several sets of points were in the glovebox when we got it, and it didn't like to start after sitting over winter unless you dinked with the points first.

    So being as GM saw fit to add HEI to their 250 sixer, we followed suit. Simple drop in right? And be sure to replace the resister wire feeding the coil from the firewall plug/block harness connector.

    I checked the coil wire with the digital multimeter. Full 12v with the key in run position. Hmm....that's odd. Has a 18g red wire that heads to the firewall connector and a yellow 16g that goes to the "start" position on the starter, both terminated in a factory connector for the coil connection.

    I remove the firewall connector and separate the yellow and red at the coil connection. Unhook the battery and backfeed the red wire 12v+ and check it at the firewall connection terminal. Still full 12v.

    Say what? So this car with original factory points had a full 12v feeding the coil.

    Now being a Volkswagen guy I don't find that terribly unusual. All aircooled VW's used full 12v to the coil, but they used internally resisted coils, thereby saving the points from the ravages of too much voltage.


    BUT BUT BUT - if GM did that on this Nova - then why is there a yellow wire to deliver full 12v from the starter "start" terminal?

    I don't get it. But it sure would explain the abundance of points both new and used in the glovebox. Apparently not a new issue.



    For the time being I added 12" of wire to the old red coil feed wire and fed the HEI with that. It reads a full 12v so why not.

    Last edited by STINEY; September 18, 2019, 06:51 PM.
    Of all the paths you take in life - make sure a few of them are dirt.

  • #2
    the ballast died, someone 'fixed' it enough to get home, then made the car somebody else's problem (a SEP car) - I wouldn't dream of doing something like that, but if I did I want it to end up on Fantomworks and listen to them bitch and moan about how terrible it is.....
    Doing it all wrong since 1966

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    • #3
      Nope that’s not the case here. Been there done that, there is always evidence of where the ballast was. Plus all the books say these cars used resistance wires.
      Last edited by STINEY; September 18, 2019, 04:03 PM.
      Of all the paths you take in life - make sure a few of them are dirt.

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      • #4
        If it has the original resistor wire, and you are measuring the voltage with it disconnected from a load, it will show 12v. If you measure it connected, with the points closed, it will show about 8v.

        My fabulous web page

        "If it don't go, chrome it!" --Stroker McGurk

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        • #5
          Ah....that’s what I was missing, a load. Doght! I knew something was fishy.

          Looks like I still have a wire to replace.

          Just out of curiousity, how much of a load would it take to change the voltage measurement? Something handy like an 1157 bulb or something more? The points closed is basically a dead short so I am guessing just a bulb is nowhere near enough load.

          i already changed the distributor months ago, been moving it around with a hunk of wire vice gripped to the battery terminal.
          Last edited by STINEY; September 18, 2019, 06:54 PM.
          Of all the paths you take in life - make sure a few of them are dirt.

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          • #6
            The coil primary winding is the load. It is similar to a 1157 bulb
            My fabulous web page

            "If it don't go, chrome it!" --Stroker McGurk

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