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  1. #1
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    MAkes no sense Mercury Tachometer problem.

    Inline 6 with thunderbolt ignition. Motor runs perfect. Have been unable to get a tachometer to work. Have done the following:

    1. Tried three different stators, all measuring at factory spec of .3-.4 ohms, even tried a brand new CDI stator.

    2. Have bypassed all the wiring on the motor and in the boat by hooking tach up to a SEPERATE 12 v Battery, running a tach signal wire to either wire from the stator. Nothing works.

    3. Tried 3 different tachs. All work FINE on another separate inline 6 with thunderbolt ignition. NONE work on this motor with the mentioned work arounds.

    4. Have tried tach connection to brown wire on switchbox. NONE WORK.

    5. Removed flywheel and tested all 12 magnets. Even switched to another flywheel that works on the other motor. NOTHING WORKS.

    This isn't rocket science, I must be overlooking something really simple. Appreciate your thoughts.

    PS one of the tachs is a brand new, just out of the box Mercury racing tach. Works fine on the other motor.

    PLEASE NOTE I have bypassed the internal wiring harness as well as the boat side wiring harness to isolate this issue. Nothing has worked.

    Time to start drinking I guess.

  2. Likes Capt.Insane-o liked this post
  3. #2
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    ALSO Resistance to ground on all stators that were tried is way up in the MEG ohms as it should be. Tried several different Rectifiers as well. all measuring out as GOOD, even the one off the engine that all the tachs worked on .

  4. #3
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    Tom you are not losing it Jeff Baker had a late 60's straight 6 do the same thing my dad let him try a used and brand new thunder bolt tach on it nothing i remembered jeff bypassed somehow and ran a separate lead for the tach to get it to work i will ask my dad tonight and hope he remembers

  5. #4
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    I have doen that, hooking the tach up right at the motor using separate power and signal wires. nothing..

  6. #5
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    Bad wiring harness shorting out the signal wire? any of the wires got the merc crumbling insulation showing?

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  8. #6
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    if you read my post I am not using ANY of th einternal wiring harness or external boat side harness at all. crumbling wires is not part of th e problem

  9. #7
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    Just grasping at straws but have you tried a different ign coil?

    Dave
    1980 Cougar 19 tunnel,90 2.4L Bridgeport EFI in middle of restoration.
    1988 BAJA Sunsport 186, 96 225 Pro Max
    79 12' Auminum, 95 Merc 9.9
    RIP Stu
    "So many idiots, so few bullets"

  10. #8
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    Sounds like a bad switch box.

    If the tach worked on the other motors with switch boxes, the stator and magnets are NOT involved.

    If the other motors had brown connected to the stator, the tach isn't going to work from the switch box and I don't know why you are having a problem getting it to work from the stator. Does the alternator produce charge?

  11. #9
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    Separate battery proper +/- , so no signal.

  12. #10
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    stator putting out about 14.5 volts at the rectifier. Have tried three different stators, same results. other motor I connected to stator lead for tach to work. Switchbox isnt in the picture unless I try to tap the signal off it which I am not doing. I did try with same results. This is an 8500 RPM switchbox.

  13. #11
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    Rectifier 100%? I had a bad regulator on my favorite 140 Chryco go bad but nothing showed except it would throw a safety switch in the black CD box to limit rpm to limp home speed after 10min running at speed. No V output problem on the gauge, everything seemed okay , bench tested it and replaced it with NOS, never threw another CD safety. Everybody thought bad CD box.

  14. #12
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    tried three different rectifiers, all measuring good onth ebench. same results

  15. #13
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    All wires to from stator, regulator, etc perfect ? I agree Makes no Sense

  16. #14
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    When you tested it with a separate battery, did you run a ground wire from the battery to the ground of the engine? you need a ground to the engine...... the harness could have a break in the signal or ground wire.
    "One of the penalties for refusing to participate in politics is that you end up being governed by your inferiors". Plato .

  17. #15
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    YEs I grounded the seperate battery to the engine. There is no HARNESS. I made a test harness of three brand new wires to run from the seperate battery to the tach and to the stator wire(s)

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