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Thread: Ballast resistor

  1. #1
    Tresguey
    What is the purpose of a ballast resistor? my friend and I have different thouights on it. He says it should drop voltage down to about 5-6 volts to the coil. i say it keeps the voltage almost to a constant voltage. or are we both wrong?

  2. #2
    sweet-v
    The idea of the resistor is that you deliberately design
    the coil to operate at a voltage lower than 12 V and then usethe resistor to get to that voltage under normal conditions.
    When you're cranking the engine with the starter the battery
    voltage drops and hence the sparks get weaker. To combat this
    you bypass the resistor as long as the starter is operating.
    This gives you pretty much similar sparks during cranking and
    normal operation. It doesn't matter if you're running
    electronic or mechanical points, it works the same way for both.
    Will this help:idea:

  3. #3
    DelawareDave
    It reduces voltage thru the coil, to around 9 volts, if memory serves me. It was to increase points life, as well as was used with the early transistorized ignitions.

  4. #4
    DelawareDave
    Sweet-v has the basic idea, except for Mopar. They used a temperature variable ballast to eliminate bypassing the resistor at start up. The longer the voltage passed thru, the higher the resistance went, up to a certain value.

  5. #5
    Tresguey
    ok, this is the iggy, my buddy just bought a engine wiring harness from Hardine marine ford 460. and the insructions it is wired in a way the the positive side of the coil gets 12 volts from the ignition switch and the I post on the starter relay gets the other side of the ballast resistor. it didnt make much sense to me. but his reply was that they made it that way for a reason. I said they were on crack and you should hit them up for frying your coil. even though it hasnt happened. i would assume it would eventualy i think. we double checked the wiring diagram on tyhe tech support online. says the same thing.

  6. #6
    Tresguey
    oh, by the way. when we hooked up 12 volts to the ballast resistor it droppeddown to i think 11.5.

  7. #7
    SmokinLowriderSS
    No resistor will not fry the coil, only burn the points up in a shorter time.
    If you switch to an electronic distrib, you no longer need the resistor, and you can still use the same coil.

  8. #8
    Tresguey
    yeah i told him to switch to an electronic ignition. but he's too cheap.
    http://www.hardin-marine.com/Instruc...ng_Harness.pdf
    here is the diagram hardine has purplewire has switched 12 volt to it.

  9. #9
    Jetaholic
    The Hardin Marine harness is wired so that the + terminal on the coil goes to the resistor, and the purple wire goes to the other side of the resistor.
    Then there's an orange wire that comes from the "R" terminal and goes to the + side as well.
    The orange wire bypasses the resistor as long as the starter is operating. Once the starter turns off, the resistor is now inline with the power feed from the key switch to the coil.

  10. #10
    Moneypitt
    Way back, 40 or so years, the big three all had their own ideas of how these ignition systems should be built and operate. The Ford/Mopar deal was to resist the voltage down, and GM used 9 volt coils. The idea that all 12 volt system coils were the same is not true. Many Chevy owners were forced to add a ballast resistor to the circuit when they purchased the wrong coil which had the resistor requirement printed right on it. If they had purchased a Delco replacement, the ballast was not required. Now, fast forward to future owners of those vehicles. Now you have an actual Delco coil, but the car has a ballast resistor???? Same could be said for a Delco coil on a Ford/Mopar......All 12 V ignition systems were not the same, and still aren't. I would suggest a "package" deal from one brand, coil, condensor, and resistor, like Mallory has sold for years. Not pushing Mallory here, they're all offshore manufactured anymore, but stick to one brand of matched componants, it will work better, (coil voltage is important), last longer, and forever take away the mix and questions about reliabilty.........Nothing wrong with a point distributor in a boat, just curve it to work in whatever set up you have and happy boating............MP

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