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  1. #1
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    Default 84 140 Hp Ignition Switch

    My 1984 Mercruiser died on me this weekend

    The engine will start and run UNTIL the ignition switch comes out of the "start" position, then it dies.

    I disconnected the battery and checked continuity between the terminals of the ignition switch and no matter the switch position there was continuity between every terminal combination....I'm betting I have a bad switch but I'm looking for confirmation.

    Also, if I test continuity from the "I" post of the ignition switch to the "+" post of the coil I have continuity....but I also have continuity from the "I" post of the ignition switch to the "-" post of the coil.

  2. #2
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: 84 140 Hp Ignition Switch

    First, is the safety lanyard hooked up? If not, the ignition will not work. Except in the start position


    Stop checking continuity, and check voltages.
    Turn the key to the run position, and on the ignition switch check for voltage on the "I" terminal (purple wire) if ok there, check on the + terminal of the coil.
    Don S.


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  3. #3
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    Default Re: 84 140 Hp Ignition Switch

    Now you'll probably think I'm a total bozo here, but I'm not sure what to use as a ground when I check voltage.

    On the ignition switch, if I check voltage from the red wire to the "I" terminal I get nothing. Checking from the red wire to the "S" terminal I get 10 volts.

    If I go back to the coil and check from the "+" coil terminal to the engine block I get 4 V with the ignition switch on and 0 V with the ignition switch off.

    Checking across the battery terminals I have around 11 V.

    Is this telling me I have a corroded copper path to the coil?

  4. #4
    Moderator Bondo's Avatar
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    Default Re: 84 140 Hp Ignition Switch

    Quote Originally Posted by w60 View Post
    Now you'll probably think I'm a total bozo here, but I'm not sure what to use as a ground when I check voltage.

    On the ignition switch, if I check voltage from the red wire to the "I" terminal I get nothing. Checking from the red wire to the "S" terminal I get 10 volts.

    If I go back to the coil and check from the "+" coil terminal to the engine block I get 4 V with the ignition switch on and 0 V with the ignition switch off.

    Checking across the battery terminals I have around 11 V.

    Is this telling me I have a corroded copper path to the coil?
    Ayuh,.... It's sayin' the battery is 'bout Dead....
    Any Grease is Better,..... Than No Grease at All.......

  5. #5
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    Default Re: 84 140 Hp Ignition Switch

    Quote Originally Posted by Bond-o View Post
    Ayuh,.... It's sayin' the battery is 'bout Dead....
    But if the battery was dead...would it crank? It turns over great, and runs fine till the key goes from start to run.

  6. #6
    Moderator Bondo's Avatar
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    Default Re: 84 140 Hp Ignition Switch

    Quote Originally Posted by w60 View Post
    But if the battery was dead...would it crank? It turns over great, and runs fine till the key goes from start to run.
    Ayuh,.... The battery should be showin' 12V, Plus.... Maybe yer meter is wrong...

    If it runs in the start position, 'n not in the run position, the keyswitch is bad, or the wirin' harness is bad....
    Any Grease is Better,..... Than No Grease at All.......

  7. #7
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    Default Re: 84 140 Hp Ignition Switch

    4 volts is pretty low. You have symptoms of bad resistor wire to the coil. When you starter is turning the coil + gets full voltage directly from the battery via a contact in the starter solenoid. When running it gets reduced voltage from the purple resistance wire. If the wire or the connection is in poor shape the engine will start and die as you describe. Your fully charged battery should read 12.6 volts, time to check your voltmeter, and if correct a load test on the battery (local Walmart, or auto parts store). Good luck.
    Terry
    87, 4WINNS H 190
    470/Alpha I

  8. #8
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    Default Re: 84 140 Hp Ignition Switch

    I fished out a different volt meter from my garage and the battery is 12.4 V.

    Looking at the electrical schematics, it looks like the wire from the ignition switch "Run" position pretty much runs straight to the "+" side of the coil with a few connections in the wiring harness.

    That said, unless someone here tells me a good reason not to do this, I'm going to run a new wire from the "Run" position of the ignition switch back to the + side of the coil and go do some skiing today, then figure out exactly where my problem is later.

  9. #9
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    Default Re: 84 140 Hp Ignition Switch

    I should also say I'm going to do some cleaning, and try to find a ballast resistor to put inline if I do run a wire from the switch to the coil.

  10. #10
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: 84 140 Hp Ignition Switch

    Find the problem, don't just start running new wires. The purple wire does more than just ignition.

    Back at the ignition switch, hook the black wire your meter to a ground on one of the gauges on the dash. Then check for voltage on the D terminal of the switch. You should see battery voltage or close to it. Then turn the key to the run position, you should see similar voltage on the I terminal (purple wire). It may show a little lower if you have an electric choke. If no voltage, you have a bad switch. If you do have voltage check the + terminal of the coil (again, black meter terminal on ground)
    Don S.


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  11. #11
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    Default Re: 84 140 Hp Ignition Switch

    I'm not sure what kind of voltage I should have from the "+" on the coil to ground, but I had 4 V and did some serious cleaning of terminals and connectors and now the voltage is up to 6.1 V and engine stays running.

    Now to adjust the idle a bit, and wait for another day to play.

    Thanks so much for all the help people, hopefully I'll be able to return the favor to someone someday.

  12. #12
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: 84 140 Hp Ignition Switch

    At the alternator, disconnect the purple wire. Turn the key to the run position and and check the wiring harness side of the purple wire (Not the wire on the alt) and see what the voltage reads.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
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