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Harness swap: Missing Pin 20 in C101

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    Harness swap: Missing Pin 20 in C101


    You can see my other thread on my injector/misfire issue, but am ultimately trying to resolve an issue with misfire/running on 3 cylinders post engine swap in my '91 325i. As part of that, per recommendation I have swapped to a different engine wiring harness (from a 1990). Unfortunately, this has lead to a host of new problems and I am about to push the car into a lake

    I swapped out the main harness, went to crank the car, and get nothing. Dash lights, etc, all fine, but no cranking. Swap relays from old harness to "new", still nothing. Check fuses, all seems fine. Battery is brand new and was firing up literally hours before. Start diagnostics and I find that I am missing pin 20 in the C101 connector.

    Doing some digging, I find that some later harnesses apparently came this way?
    SO, do I need to hack into the harness side of the C101 and run a pin from there back to the dme connector (which I also don`t want to really hack into)? Suggestions on this one? E30 Zone wiki has some slightly confusing verbiage on this, so looking for anybody that has encountered this and how they resolved it!

    This does not resolve my current no crank situation, but I have more diagnostics to do in tracking that one down....Either way, want to resolve this piece

    Last edited by gybe,; 04-28-2020, 08:11 AM.

    #2
    Pin 20 can either be power, ground, or empty depending year. In '91, pretty sure pin 20 is ABS power on late models, so you can just grab power for an adjacent wire.

    EDIT: Power comes from pin 87 of the main relay:



    The car will run fine without pin #20, but the ABS naturally won't work.
    john@m20guru.com
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    Transaction feedback: Here, here and here. Thanks :D

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      #3
      Originally posted by ForcedFirebird View Post
      Pin 20 can either be power, ground, or empty depending year. In '91, pretty sure pin 20 is ABS power on late models, so you can just grab power for an adjacent wire.

      EDIT: Power comes from pin 87 of the main relay:



      The car will run fine without pin #20, but the ABS naturally won't work.
      In other words, as I suspected, that is not the source of my overall power issues. Ugh

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        #4
        I am a much bigger idiot, I really have to stop working when I am tired. My measurements of voltage were bunk, so disregard those for now

        Regarding taking power from somewhere else for Pin 20, any suggestions there?

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