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Ignition switch bad?

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  • Ignition switch bad?

    1987 Merc 165, (470), Alpha 1 Gen 1

    Good morning all,
    I'm checking the continuity between the switch terminals on the back of my ignition switch according to my manual (No. 8).

    The back of my switch is configured differently and my wire colors are different than how the manual shows, so I wanted to see if anyone could tell me what correlates to what.
    Reading from 12 o'clock and going clockwise the manual has:
    I, A, B, and C terminals

    Reading from 12 o'clock CW my switch has:
    IGN, BAT, SOL, and ACC terminals

    I assume that I=IGN, BAT=B, ACC=A, and SOL=C

    Is this correct?

    With my ignition switch at the "start" position I'm getting continuity from B to all terminals except C. The test was made with the switch removed.

    My reason for checking the switch is that my engine will run while the starter is engaged; however, when I let off the key (when the ignition switch is in the "RUN" position), the engines dies.

    Thank you for your help.

  • #2
    Re: Ignition switch bad?

    On your "470" the coil gets its power from the slave solenoid bolted to the block during starting. Through the purple resistance wire (from the choke) when the ignition is on. Sorry got that wrong before.
    87, 4WINNS H 190
    470/Alpha I


    • #3
      Re: Ignition switch bad?

      Originally posted by stonyloam View Post
      On your "470" the coil gets its power from the slave solenoid bolted to the block during starting. and through the purple resistance wire when the ignition is on. Sorry got that wrong before.
      Check out the diagram on page 4E-7 of your manual. The purple resistance wire from the choke provides voltage to the coil when ignition is on. When the ignition is on, you should have +12v at all of the purple wires. Check for 12v at the choke, and if there check for voltage (probably less than 12v) at the + terminal of the coil. Sorry about the screw up above.
      87, 4WINNS H 190
      470/Alpha I


      • #4
        Re: Ignition switch bad?

        I appreciate your help. I will check my voltage again at the coil.

        However, I just checked the continuity at my kill switch. With the cap on, (as if underway), I have continuity, and with the cap OFF, I don't. This is opposite of how it should be. I have another kill switch handy that tests OK and will replace with it.

        Maybe the bad kill switch is allowing the engine to start while cranking, but killing it when the key is released and in the RUN position?


        • #5
          Re: Ignition switch bad?

          Here's my voltage at the coil:

          While cranking I have 10.6 V at the pos terminal and 8.4V at the neg terminal.
          With the key in the "run" position I have 0V at each terminal.

          Also while cranking, the voltage at the slave solenoid is 10.6V (terminal with purple/yellow stripe wire).

          Voltage at the red wire terminal (going to battery) is 12.6V.

          Are these voltage readings correct?
          I have ruled out the ignition switch and kill switch. When cranking, the engines starts briefly and then dies.
          I'm getting two good streams of fuel into the carb. I have the pertronix elec. ignition with timing at 8 degrees TDC. Using a timing gun, I have a spark going through each wire. I have a blue spark from my center distributor wire to the block.

          Please provide any suggestions for what to check next. I'm stuck.


          • #6
            Re: Ignition switch bad?

            Your safety 'kill' switch is working fine, your ignition key switch is working fine. You have a break in the resistance wire somewhere between the electric choke and the coil.

            As a quick test just run another piece of wire between the choke and the + on the coil.

            The world takes on a whole new perspective when viewed from 100 below.
            1972 Bertram Bahia Mar 20
            2006 Mercruiser 4.3MPI (0W617679) w/Alpha One Gen II (0W829301)
            (Original - 1972 '165' In-line 6. Previous - 1994 4.3LX)


            • #7
              Last edited by SSTKO81; July 6th, 2010, 10:05 AM. Reason: want to repost elswhere
              It's like Murphy's law, but worse; another T.K.O>


              • #8
                Re: Ignition switch bad?

                Well friend, you were right. I ran a jumper from the choke to the coil and she fired right up.
                Thank you and I hope to be able to help you one day.


                • #9
                  Sign up today
                  Re: Ignition switch bad?

                  I checked my ignition and kill switches for continuity. Then, from Stonyloam's advice I went to the engine to check voltage at the coil when cranking. (I hooked up a remote starter switch from the ignition to let me reach back there). I also checked the voltage at the slave and starter solenoids.
                  I had low voltage on the purple wire at the coil, and as Chris suggested, I ran a jumper from the choke to the + terminal at the coil. And she started.