Factory tach with aftermarket HEI

Discussion in 'Troubleshooting & Diagnosis' started by Elliott Taylor, Dec 17, 2020.

  1. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    I’ve heard people have had problems with an MSD ignition system and the factory tach but a “normal” HEI will work fine.
     
  2. COPO

    COPO Veteran Member Lifetime Gold Member

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    My Tach wire on my 70 is connected to the MSD 6AL Tach terminal cause it would not work in the factory position on the coil.
     
  3. biker

    biker Veteran Member

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    My 77 Z came factory with HEI. Then went to DUI HEI, plugged right in and tach worked fine. Same with my 81.
     
  4. Elliott Taylor

    Elliott Taylor Member

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    Awesome. I feel better about the whole issue now
     
  5. Coadster32

    Coadster32 Veteran Member Lifetime Gold Member

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    I also have a 6AL MSD box, hooked to the brown tach wire with factory tach. No issues.
     
  6. Chuck71RS

    Chuck71RS Veteran Member Lifetime Gold Member

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    Having idiot lights and the large fuel gauge, you will need to replace the printed circuit on the back of the instrument housing. Tach and full gauges is part of the u14 set up

    My 71 Camaro had indicator lights-large gauge and I had to change the printed circuit. Some additional wiring changes were needed to the 12 pin plug that inserts into the pc. You will find a sticky about this in the Electrical section but some of the plug wiring might be different for your 1977. Compare a 77 wiring diagram to the sticky

    If the tach needs servicing contact tachman.com. Daniel (Gauge Marks) has retired. His email address is no longer valid. I sent him an email a month ago and it was returned as not a good address.
     
    Last edited: Dec 19, 2020
  7. joer

    joer Veteran Member

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    Did you cut out tach filter? or just cut off end and splice new wire to MSD box.
     

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