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Thread: HELP! Mystery Connector on '98 540i Engine Wiring Harness

  1. #1
    Join Date
    Nov 2003
    Location
    Irvine, CA
    Posts
    537
    My Cars
    1998 BMW 540i

    HELP! Mystery Connector on '98 540i Engine Wiring Harness

    I'm hoping one of you guys with an early-model 540i can pop the hood and help me out with this, or just happen to know what it is. I just finished doing a valley pan replacement on my car, and was scrupulous in labeling all the wires and connectors on both sides, but when I finished, this one was left, and as short as it is, with no apparent place to plug in. It has one red wire with a white stripe, and one blue wire with a yellow stripe.

    As you can see in the pic, it is in the topmost wiring loom coming out of the passenger side injector electronics box, and is wrapped with three other wires/connectors - one goes to the Idle Control Valve, a second goes to the Primary Throttle Body Throttle Position Sensor, a third goes to the Secondary Throttle Body Throttle Position Sensor.

    I don't know where this one goes - all the sockets I can find are already occupied, including the mapping thermostat. It could be that it was never plugged into anything - it's pretty dirty inside and out. Anyway, I'd be grateful for any help, even if it's just knowing that it's supposed to be unused.

    Thanks in advance for any help.
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    Last edited by Hotswimmer; 07-16-2006 at 08:56 PM.

  2. #2
    Join Date
    Mar 2005
    Location
    tennessee
    Posts
    11
    My Cars
    94 mazda rx7, 98 BMW 540i, 96 Audi A4,89 VW GTI
    mine has the same connector, it does not go to anything. My car has never been taken apart.

    1994 rx7 twin turbo base model
    chaste white
    R1 front and rear spoilers
    racing beat springs
    tokico 5 way adjustable shocks
    rx7 store downpipe
    resonated midpipe
    Greddy SP cat back
    Pettit HOT air intakes
    Apex'i GT spec FMIC
    Apex'i power FC
    E-bay power pullies
    fluidine radiator
    supraTT fuel pump
    Spec stage 2 clutch
    17" Borbet type t wheels

    BMW 540i
    automatic
    107k
    silver with grape ape interior

    a few beaters

  3. #3
    Join Date
    Nov 2003
    Location
    Irvine, CA
    Posts
    537
    My Cars
    1998 BMW 540i
    Thank you, Scott - I owe you big. I was seriously stressing...

  4. #4
    Join Date
    May 2015
    Location
    Victoria BC Canada
    Posts
    201
    My Cars
    1998 BMW E39 540i
    I have found the definitive answer to this question. These wires go to the vacuum valve for the secondary air injection, if you don't have secondary air injection this plug will be left disconnected at the factory.
    http://cdn4.pelicanparts.com/techart...arge/pic01.jpg

  5. #5
    Join Date
    Sep 2010
    Location
    Ooltewah, TN
    Posts
    2,527
    My Cars
    2010 BMW M6*2019 X3 M40i
    As with many cars, this is quite common. Model changes, engine changes, accessories changes etc... It's much cheaper and simpler for manufacturer to produce wiring harness with extra connectors instead changing it half way through production or for some other reason.
    Since I have the same car, I think I remember that extra connector as well. I love the fact that 98 has no secondary air injection vs 99+.
    Last edited by BMW540san; 03-13-2017 at 09:08 AM.

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