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M42 Engine Harness Removal Question

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    M42 Engine Harness Removal Question

    Hi r3v,

    I'm currently diving into my first ever engine swap in a 1991 318is. Since the M42 got destroyed by the previous owner, I am planning on doing an M52 swap. The reason I'm in the M42 sub-forum is because I am confused about the M42's wiring. The engine is out of the car, but the engine harness is still in there. I'm not entirely sure what the wires are that run into the fuse box do (Not the C101, but the wires right to the right of the C101). I am also confused about what the little module that looks like it has a few ground wire connections going to it that is directly to the left of the heater core and sort of above the other battery tray in the engine bay. The rest of the harness was fairly easy to undo, but I'm just confused about the portions of the harness I listed. This is my first time doing any sort of engine swap electrical so bear with my lack of knowledge. Thanks!
    1990 Brilliantrot 325i Coupe AKA Whitney - sold :(
    1991 Brilliantrot 318is Coupe

    #2
    Can you snap a couple of photos of what you are looking at?

    Stuff to the left of the heater core / above the battery tray includes the battery lug for the starter, as well as a separate power connection for the fuel injection electronics. A few of the larger wire splices where multiple grounds and power lines come together have rubber caps over them.

    On the fuse box side, the stuff coming out of C101 is the connection between the ECU and instrument cluster, as well as the fused portions of the injection system, air conditioning switches, etc.

    The full factory diagram for the E30 M42 is here:


    Also, when I was planning to go with an aftermarket ECU, I completely unwrapped and diagrammed a factory harness. It is a little rough, and although I did double check everything, it might not be perfect...BUT, in a couple of places where the wire colors differ from the "official" diagram, mine is actually correct since BMW made errors. Apologies for the immense size (13345x7484px), I had planned to print a D-size version for when I modified my harness.

    Transaction Feedback: LINK

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      #3
      That diagram is awesome!

      OP, pics will certainly help us answer your questions.

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