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Tachometer quit working

Discussion in 'Post Yacht' started by JFpost, Feb 8, 2026.

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  1. JFpost, Feb 8, 2026
    #1
    JFpost

    JFpost New Member

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    I have a 1978 Post with 6-71 ( non -turbo) and the port side tach quit working. I replaced with new tach and still not working, not getting a signal to it. Anyone ever have an issue like this? I’m sure with some tracing the wire down I can figure it out, was hoping someone may have had this issue before.
  2. MBevins, Feb 8, 2026
    #2
    MBevins

    MBevins Senior Member

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    Is it getting feedback from the alternator?
    Quite common.
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  3. Capt Ralph, Feb 8, 2026
    #3
    Capt Ralph

    Capt Ralph Senior Member

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    Other than the alternator, the 6-71 usually uses a maniacal tach pick-up for the electronic tach.
    Question one; Do you use a mechanical engine synchronizer? Is it workings?
    If no synchronizer, you may find a tach pick-up on the back of the engine with a couple of wires to it.
    There are other ways to get a a signal to the tach.
    Including a pic-up on the front pulley or even a tap in the bell-housing.

    Let us know what you have to help save time to help.
    Last edited: Feb 8, 2026
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  4. JFpost, Feb 12, 2026 at 2:14 PM
    #4
    JFpost

    JFpost New Member

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    It isn’t. Just drops to zero..
  5. JFpost, Feb 12, 2026 at 2:18 PM
    #5
    JFpost

    JFpost New Member

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    So I do use a mechanical synchronizer and it works fine. The port side tach was bouncing around and then just stopped, so I replaced and wired up same exact way but it does t respond at all. Starboard has no issues. Thank you
  6. Capt Ralph, Feb 12, 2026 at 8:53 PM
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    Lets try again.
    Not an alternator feed?
    Synchronizers are working. Is there a tach sender on the sync box ?
    Or somewhere else?

    Lets identify the tach sender and troubleshoot from there.
  7. JFpost, Feb 12, 2026 at 9:55 PM
    #7
    JFpost

    JFpost New Member

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    Honestly I will have to look ( sync box) that’s a great question. When I was trying to trace the wires I didn’t even look at that, I will be back in town this weekend and hopefully will have a chance to look at that. I will also try and get a few pictures of the tach, alt as well..I am not sure if alt or elsewhere. I am familiar with diesel engines ( trucks) and while mostly the same, I realize there are some differences in the marine diesel and I am still playing catch up on the electrical and a few other things. I certainly appreciate the help and will look at that and respond back. Thank you
  8. Capt Ralph, Feb 13, 2026 at 8:07 AM
    #8
    Capt Ralph

    Capt Ralph Senior Member

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    Detroits are great engines. NOT a lot of wires go to them..☺☺