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  1. #1
    FEP Supporter vdubn's Avatar
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    Default MSD Digital 6, Do I need a Tach Adapter, Which is the Tach Lead

    So, I got my 1985 GT (converted over to EFI with full 86 harnesses) fired up for the first time last night, and it runs great, but has a few wrinkles to work out.

    First is the fact that my factory tach is not working. After some research, it looks as though I may need an MSD Tach Adapter, part number 8920. I am running an MSD Digital 6 (not to be confused with the 6A or 6AL series MSD systems), and I am having a tough time finding accurate info as to what I need, and how to connect it to my car. I called MSD today, and they said that they couldn't give me any specific information about how to wire it to my car, but they said just don't connect the Tach Adapter to the coil... AT ALL. MSD shows wiring diagrams to connect their Tach Adapter to a 6A or 6AL, but nothing for the Digital 6.

    This was especially confusing, as I thought that the tach lead in our cars connected to the negative side of the coil.

    The Digital 6 has a tach lead connector, so I can wire the Tach Adapter to that, I just need to know what signal wire I need to connect the Tach Adapter to, so that it will send my factory tach the appropriate signal.

    Hopefully someone has been through this, and can help out.

    Thanks in advance
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  2. #2
    FEP Supporter vdubn's Avatar
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    I found this diagram, that shows the tach signal wire (Dark Green, With Yellow stripe) goes to pin 4 of the EEC, and I assume that it also goes to the Tachometer, right? I also need to find out if I can connect this wire straight to the tach output on my MSD Digital 6 Plus, or will I need a Tach Adapter to bridge between the MSD and my factory tach? Also, if I clip this wire from the negative side of the coil, will it cause any issues? I can do some testing tonight to see, just curious to hear from anyone else who has run into a similar situation.

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    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  3. #3
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    Really surprised that MSD's Tech support can't help you. Have you tried giving them a second call to see if you get a different tech support person? Might get a better answer form a different person. Wish I could help. I have the 6AL programmable box so hopefully I don't run into the same issue.

  4. #4
    FEP Supporter vdubn's Avatar
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    Yea, I was surprised as well. You would think they could get any information for any vehicle, especially the cars that they market their products to... I think that I may have it figured out though. I will post back how I had to wire it all to get it to work.
    85 GT Hatchback, T-Tops. Rebuilt 302, 10.6:1, Edelbrock Alum heads, Performer Intake, full EFI swap from 86, 3.73 Posi 8.8, 5 lug Cobra 13" fr and 12.6" rear disc swap, MM SubFrame Connectors, MM Panhard Bar, MM front A-Arms, MM rear control arms, Raceland Coilovers, T5 with Centerforce DF Clutch.

  5. #5

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    1986 GT T Top- stock except for magnaflow cat back
    1990 LX vert- 500hp V3 and all that stuff
    2013 GT- usual bolt ons

  6. #6
    FEP Supporter twinturbohow's Avatar
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    This probably won't help much but I found in some notes I made about a white wire going to the tach adapter. I'll see if I can dig any more up.

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