Coil is very hot

Discussion in 'Softail Models' started by BigBiker, Dec 7, 2008.

  1. BigBiker

    BigBiker New Member

    Hello Glider, i`m new on this site and i have a strange problem on my `92 fatboy.
    I`ve installed a couple of weeks ago a new horn and i have to remove the fueltanks because i don`t want to see the wires.
    After all,i mount the fueltanks and everything is fixed now, but when i touched the spark coil,it was so hot i couldn`t put my hands on it.
    The engine`s off and the ignition switch is on and only when i turn the switch a little bit back,i can hear a little noise in the coil.
    When i push the engine`s stop-button, there`s no voltage on the coil also.
    I have checked the wires to find out if there`s a connection or broken wire or whatever ,but everything seems to be okay.
    I have really no idea how i can fix this problem.
    After all,since i find out that the coil`s getting hot, there`s a detonation sound in my engine.
    Could there be a possibility?
    Glider, the last thing i want to say is thank you for your help.

  2. glider

    glider Veteran Member

    Coils do operate hot once they have been energized for a while. Check the polarity of the coil to see if you have the hot wire on the + side of the coil.

    Do you have a schematic for the bike?

    If not there may help you out.

    Wiring Diagrams Online - Harley Davidson Community

    This schematic should be very similar to your bike.

  3. dangerdan

    dangerdan Junior Member

    I would also check coil resistance on primary and secondary of the coil.

    Values should be within 5% - 10% as stated in the manual.

    Also try this with the coil cold. Get a spray bottle with a fine mist and spray the coil while the bike is running. If you see any type of spark discharge or spark, its safe to say the coil is bad.
  4. BigBiker

    BigBiker New Member

    Dangerdan,thanks for your information.
    I`ve checked the coil and the servicemanual says that the primary side have a range of 2,5 to 3.1 ohms and the secondary 11.250-13.750 ohms.
    I`ve tested the coil in cold position and these are the next results:
    primary 4 ohms secondary 11 ohms.
    after that i tested the coil in warm/hot position ( it took +/- 12 minutes to reach that) by only the ignition switch on and the engine off,and these are the next results:

    primary 5.25 ohms secondary 12.92 ohms.

    Is that normal?
  5. dangerdan

    dangerdan Junior Member

    The book says 2-3 ohms primary and 11k - 13k secondary .

    Primary (5.5 ohms) is ok
    Secondary should read 11k - 13k not 11-13 ohms. I think you meant to use a "COMA" not a "PERIOD"
    If your getting 12.9k ohms on secondary you should be good, but if your only getting 13 ohms on the secondary, the coil needs replacing.
  6. BigBiker

    BigBiker New Member

    DangerDan, you`re right.
    I`ve made the mistake with the ``Period,, instead of the ``Coma,,it`s definitely
    13k ohms.
    Thank you for your cooperation.