205 coil - with resistor or without
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  1. #1
    Fellow Frogger! spar's Avatar
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    Default 205 coil - with resistor or without

    When buying a new coil which one should i get?

    Couldnt see from markings on the existing coil.

    cheers
    Shane

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  2. #2
    Fellow Frogger! spar's Avatar
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    What does the Ignition Coil Resistor do?
    when you are starting (the starter is running) a car/truck available voltage drops down because of the electrical load from the starter to about 9 volts. this would be a problem if the ignition system (coil and points/ignition module) was set for 12~14 volts as at 9 volts you may have no spark, so they set the voltage at 9 volts all the time and use the resistor or a built in voltage regulator in the ignition module to bring the voltage down when the car is running and give it full voltage (9 volts) directly when the car is starting usually thru a bypass wire or switched connector.
    so does a standard 205 gti have a resistor wire or does it require a coil with a resistor built in?

    any clues? the haynes shows a completely different style of coil - with a 4 pin plug, my car just has a standard old school type bosch cylinder jobbie.

  3. #3
    Fellow Frogger! spar's Avatar
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    well i found my multimeter so i'll just post this in case someone else ever googles and needs to know - 12V LT to the distributor so resistor in system not in coil.
    Last edited by spar; 18th September 2011 at 09:09 AM.

  4. #4
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    Default Measuring Voltage at Coil

    Hi.

    I don't know if your 205 needs a 9 volt or 12 volt coil. However when measuring supply voltage to the coil terminal, you must take the measurement with the coil under load, and not just the open circuit voltage. Even if the supply cable is a resistance wire, you will still record battery voltage (12V) to earth if there is no load (current) on the circuit to make the resistance. Remember Ohms Law formula V = I x R.

    From your reply I was unsure as to how you obtained the measured voltage.

    Sometimes a coil had an R incorporated into the part number stamped, often into the base of the coil.

  5. #5
    Fellow Frogger! spar's Avatar
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    Quote Originally Posted by Whippet View Post
    I don't know if your 205 needs a 9 volt or 12 volt coil. However when measuring supply voltage to the coil terminal, you must take the measurement with the coil under load, and not just the open circuit voltage. Even if the supply cable is a resistance wire, you will still record battery voltage (12V) to earth if there is no load (current) on the circuit to make the resistance. Remember Ohms Law formula V = I x R.

    From your reply I was unsure as to how you obtained the measured voltage.

    Sometimes a coil had an R incorporated into the part number stamped, often into the base of the coil.
    ok, perhaps i was measuring incorrectly but i understood it was the wire (low tension lead?) from the coil to the dizzy was 12v or 9v at the coil end.

    expressed otherwise you would say it's whether the wire from the coil to the dizzy had resistance or not.

    isnt the idea that when under load the other end will stay at 9v?

  6. #6
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    On a negative earth system the (low tension) battery voltage (or 9V) is supplied to the + terminal on the coil. The coil circuit to earth is completed through the distributor.

    Therefore under load (with the points closed) you should expect battery voltage (or 9V) on the + supply to the coil, and hopefully 0V on the -terminal. The wire from the coil to the distributor should have virtually no resistance.

    On early Holdens and Fords etc it was usual for the 9V coil to have two wires connected to the +terminal. One from the ignition switch which was ni-chrome resistance wire, and the other from the starter motor which supplied battery voltage while the engine was being cranked.

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