1957 Mercury Mark 75 resistor issue

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  • July 4, 2026 at 6:08 am #323602
    Cjbrill715
    Participant

      When my key is left in the on position, one of the resistors glows red hot. Is this just the nature of the beast with this ignition system (meaning I should be intentional about always bumping the key back to off position) or should I be looking for a dead short somewhere?

      July 4, 2026 at 9:18 am #323619
      DAVID
      Participant

        US Member

        YES!

        July 4, 2026 at 11:22 am #323626
        Tubs
        Participant

          In a points ignition there is a resister used to keep the points from burning up. The resister does get very hot. The points completes the circuit when they are closed. Even though the resistor may reduce the voltage by half, or more. leaving the key on, when the motor isn’t running, can still damage the points. It doesn’t do the resister any good ether.

          A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.

          July 7, 2026 at 8:05 am #323969
          JACQUES
          Participant

            He is what I did  on my lawn tractor…after I found it resting KEY ON a week later .  The seat safety  switch had done its job and turned of the engine after I got off the tractor….with me forgetting & leaving the KEY ON !!   DEAD BATTERY after a week

            I installed a cheap 12vdc  3-4 $ piezo buzzer  across  KEY on power  and  LIGHTS ON switch positions to make certain I would hear the buzzer if ever the engine was not running! .

             

            The buzzer is not to loud and I really do not hear it over  engine  running noise… but I sure do hear it when the tractor  anytime   it is  “left key-on/not running”   same for the lights !

            To  prevent any backfeed between the two B+ sourcess I wired in 2 diodes …both converging on the buzzer .   Either condition will alert me if the engine is not running with  key left ON …same for lights  

            a KEY ON buzzer  on the KEY ON lead  installed under the cowl will always sound off  but get muffled away   with engine running.  If the engine stops  with key ON  you will get a reminder to turn off the switch !!

             

             

            Joining AOMCI has priviledges 🙂

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