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Thread: 85 Electronic Cluster - Convert to tach - shows only up to 2250 RPM

  1. #1
    ...if you know what I mean... Turbo Mopar Contributor csxtra's Avatar
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    85 Electronic Cluster - Convert to tach - shows only up to 2250 RPM - Solved

    I have a 85 turbo NYer with the electronic cluster and I want to replace the Message Center with a tach from a 600ES electronic cluster.

    I took the cluster apart and unplugged the message center and plugged the tach in where it is marked "tach" on the board. Put the cluster back in the car and the tach LEDs only light up to 2250 RPM and above that it flashes and goes out until the revs drop again. The LEDs over 2250 RPM never light up, regardless of engine RPM.

    I have tried it with two separate tach modules, both do the same thing. I looked at the main cluster circuit board and the only thing I found is a 3-conductor ribbon cable that plugs into a connector with 6 pins. The connector is plugged into the three pins that are towards the right side of the car, does that connector have to be moved to make the tach work? I haven't found anything in the FSM about it.

    I was hoping that just replacing the message center with the tach module and replacing the bezel would work, is there something else I am missing?

    Thanks in advance for any help you can provide,
    Warren
    Last edited by csxtra; 08-21-2020 at 08:26 PM.
    Warren Hall
    "My Name is Warren and my car is an alcoholic..."
    OVC - SDAC "Our Sh*t Rolls!"
    Cincinnati, OH
    87 CSX # 741
    317WHP - 380 WFt-Lbs (STD-5)
    12.460 @ 113.2 - Race Gas + Methanol Injection
    12.749 @ 109.84 - 91 octane + Methanol Injection (Still tuning...)
    "Illegitimi non carborundum."
    -General Joseph Stillwell
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  2. #2
    Hybrid booster Turbo Mopar Contributor 85lebaront2's Avatar
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    Re: 85 Electronic Cluster - Convert to tach - shows only up to 2250 RPM

    Ok, first have you tried running the built in diagnostic tests? Those test every component of the cluster and the LEDs in the tach boards seem to be problematic. When I acquired a tach module for my 1985 Lebaron convertible I had to resolder almost every one of the LED joints. I still have my 1985 cluster, my current project I have put a 1989 J body dash in the 1986 K body convertible.

    I can get some pictures of the cable connections on my cluster.

  3. #3
    ...if you know what I mean... Turbo Mopar Contributor csxtra's Avatar
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    Re: 85 Electronic Cluster - Convert to tach - shows only up to 2250 RPM

    Thanks for replying, no I haven't run the built-in diagnostic tests yet. I will do that before doing anything else.

    I wasn't sure if there was something on the main board that had to be changed to get the tach to work correctly and saw those 3 unused pins on the J5 connector and started to wonder if something was missing or needed to be changed, since both tach modules exhibited the exact same behavior.

    I will also resolder the LED joints. Did you have to resolder the common side of the LEDs in addition to the joints that go into the tach board?

    Pictures would be great if it is not too much trouble!

    ===========
    Update: I ran the built-in diagnostic tests, and most of the segments lit up on the tach but some were very intermittent, so it looks like the board is driving the tach correctly, but some of the LED connections are questionable.

    Out comes the soldering iron!

    I will re-test after resoldering the LED connections.
    Last edited by csxtra; 08-21-2020 at 01:12 PM.
    Warren Hall
    "My Name is Warren and my car is an alcoholic..."
    OVC - SDAC "Our Sh*t Rolls!"
    Cincinnati, OH
    87 CSX # 741
    317WHP - 380 WFt-Lbs (STD-5)
    12.460 @ 113.2 - Race Gas + Methanol Injection
    12.749 @ 109.84 - 91 octane + Methanol Injection (Still tuning...)
    "Illegitimi non carborundum."
    -General Joseph Stillwell
    TD Runlogger Page Has Moved...

  4. #4
    ...if you know what I mean... Turbo Mopar Contributor csxtra's Avatar
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    Re: 85 Electronic Cluster - Convert to tach - shows only up to 2250 RPM

    Issue solved: the problem was the tach driver on the cluster main board. I resoldered all the LEDs and the problem was still there. I put the tach module onto a spare cluster I had and now the tach works just fine.

    Thanks for the help, I greatly appreciate it!
    Warren Hall
    "My Name is Warren and my car is an alcoholic..."
    OVC - SDAC "Our Sh*t Rolls!"
    Cincinnati, OH
    87 CSX # 741
    317WHP - 380 WFt-Lbs (STD-5)
    12.460 @ 113.2 - Race Gas + Methanol Injection
    12.749 @ 109.84 - 91 octane + Methanol Injection (Still tuning...)
    "Illegitimi non carborundum."
    -General Joseph Stillwell
    TD Runlogger Page Has Moved...

  5. #5
    Hybrid booster Turbo Mopar Contributor 85lebaront2's Avatar
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    Re: 85 Electronic Cluster - Convert to tach - shows only up to 2250 RPM

    Ok, sounds good! Keep in mind we are dealing with 30 + year old electronics on these cars and in your case a failed tach driver wasn't obvious as it wasn't being used.

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