I know we beat this to death but....

Electrical & Ignition

  1. jake

    jake Senior Member

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    Ballast resistors. I am starting to blow them constantly, frying coil, and it is starting to become scary when the motor stops, my brakes dont!!! 13.73v in and almost everyone I have gotten out of the box leave around 11.11 volts. I thought you should be getting 9volts out of the resistor. Bought them from Rockauto, autozone, amazon, summit, ru-11 i think. Orange ecu and mopar electronic conversion. Any ideas would be great. Did the 90 mile round trip to Volo show with no problems, had no issues for quite some time. Put new coil on also.
     
  2. Polara_500

    Polara_500 Senior Member FCBO Gold Member

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    Sounds like something's wired around it.
     
  3. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    I am thinking the ballast resistor is bypassed somehow as noted. Turn on the key and check the voltage to the coil it should not be battery voltage except when the key is in the start position. Could the run and start wires to the resistor be reversed? Usually there will be a two wire connection on the exit side of the resistor, one wire is the ignition start circuit at battery voltage, the other goes to the coil. On the entry side of the resistor is a single wire for the run connection, this lead has the current reduced by the the resistor.

    Dave
     
    Last edited: Jul 15, 2019
  4. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    The resistor limits current, not voltage.

    Measure the resistance of the ballast resistors, not voltage. The voltage will be higher when there is a lower current draw and higher when there's a higher current draw. Basic electricity.

    You say you are "blowing" coils or ballast resistors?
     
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  5. jake

    jake Senior Member

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    8.5 volts to the coil with key in. I do have the 2 wire connection on the leaving side of the coil. Is it frigging possible to get that many bad resistors?
     
  6. jake

    jake Senior Member

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    Wrong use of words. I have tested the resistors with ohm meter and i get 1.3 on some and up to 2 on others. I assume they heat up, the resistance lessens?
     
  7. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    It sounds like it is wired properly then. You replaced the coil, probably was shorted and overloading the resistor. Or the coil was just going to ground and it stopped functioning.

    Dave
     
  8. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    Generally speaking, the resistance will increase with heat.

    1.2 ohms is the nominal, so 1.3 ohms sounds good. Does the ballast resistor test "open" after your failure?

    Explanation of voltage drop with ballast resistor.

     
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  9. fury fan

    fury fan Senior Member

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    All of this makes me love my MSD-6 - no resistors, no Mopar-type ECU that is of sometimes of poor longevity (according to some websites, anyway), and I have a big 'ole spark jumping across an .060" gap. Have been a fan of MSD stuff since my first one in 1997.

    My recommendation to anyone who doesn't mind the non-stock appearance.
     
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  10. tbm3fan

    tbm3fan Senior Member

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    Same as me with my HEI. No more worries when a Pertronix might fail again in my Dodge product.
     
  11. fjr

    fjr New Member

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    The previous posts have good advice. The ballast resistor limits current to the coil at low RPMs to keep it from oveheating and burning out. I've upgraded my car to the HEI system from the Mopar electronic ignition to get a hotter spark so as to be able to run leaner cruising fuel mixtures. The HEI module has internal circuitry to limit coil current and therefore does not require a ballast resistor. Here a write-up about my ignition system: HEI Ignition Upgrade
     
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  12. fury fan

    fury fan Senior Member

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    One more detour, but a cool thing about the MSD system -

    There's an adjustable timing module that will allow up to 15deg of retard via a knob. (it will not advance)
    If you advance your dizzy by 15deg, though, then keep the knob retarded, you effectively make it an advance adjustment.

    Why bother?
    Well, on my 1/2-worn out stuff, when the engine is cold, or in cold weather, they run SO much smoother with an additional ~10 deg of ign advance.
    Then simply turn the knob back as things warm up. If you forget (and I have) the spark knock rattle will remind you.
    It could also be wired thru a relay to only be active when the engine is cold. Relay coil is ign powered, with ground side of coil triggered by a coolant temperature switch. (watch polarities and NO/NC on everthing so it turns on/off the way you want)


    upload_2019-7-24_18-37-42.png
     
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  13. Mike66Chryslers

    Mike66Chryslers Well-Known Member

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    Did you replace the coil first, and then you started blowing BRs? Stock-style coil or "performance" aftermarket coil? What was the internal resistance of the old coil and what is the internal resistance of the new coil?

    Mopar electronic ignition conversion kits included a new BR in the kit. Unless you're running some kind of low resistance coil, (some of which have a BR recommended by the manufacturer) you should probably be running the same resistance that the kit BR had. I don't know what value it is offhand.

    Do you sometimes leave the key in the ON position for extended periods without the engine running?

    Have you wired anything else up to the circuit from BR to coil+ terminal, such as an electric choke?