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Thread: Tachometer input wire?

  1. #1
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    May 2014
    Portland, OR, USA

    Default Tachometer input wire?

    My 280Z uses an MSD 6A ignition. I need to hook up the tachometer, but I don't know what to do.

    More specifically, the 6A has a grey wire that is related to the tachometer. I imagine the tachometer has some input wire that is looking for a specific voltage. My 6A is in my engine bay on the right side (near the relay box). Is there some convenient way for me to hook this up? I would prefer not having to run a wire through the firewall and splicing stuff onto my tach.

    Also, I do have the 8910 MSD module that is apparently required for correct functioning.


    EDIT: Here is what I see in the relay box: I'm hoping I can use one of these. Thanks again!!
    Last edited by aochider; 06-06-2014 at 11:13 PM.

  2. #2
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    May 2014
    Portland, OR, USA


    Hate to reply to my own thread (mods please correct this if it's not allowed), but I solved the problem.

    The stock 1978 280Z tachometer needs the MSD 8920 tach adapter. I am using the MSD 6A ignition module (the new one with the detachable harness), with a Holley carbureted L28. This makes sense because MSD's own table ( says to use the 8920 for magnetic triggering, but for some reason everyone seems to say 8910 for the 280Z.

    Anyway, I just wired it up as it showed in the MSD manual:

    * Grey 6A wire to White 8920 wire to grey 6A wire (6A manual says that is the tach wire)
    * Purple 8920 wire to your tachometer input (very last blue wire in the main harness. Follow the thick harness from the passenger firewall all the way to the passenger headlight, in front of the radiator, to the driver headlight, and then finally to the coil area. The longest blue wire in that is the tachometer input. I believe it originally goes to the coil, but my car was never wired that way since I owned it.)
    * Red 8920 wire to 12v ignition wire (I just used the same one that the 6A is using)
    * Black 8920 wire to ground

    I measured the grey 6A tach wire and saw it was outputting ~6v at idle (~1k RPM). The purple 8920 wire was putting out ~13v to the 280Z tach wire. This seems to be the purpose of the adapter.

    All this seems kinda obvious now, but I hope it helps someone else later!
    Last edited by aochider; 06-07-2014 at 06:27 PM.

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