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    Trunk Lid light extra wire

    I also posted this as a reply/question in Car & Audio on a thread about adding a second trunk light.

    My problem is that the trunk light was staying on even with the lid closed. 1st guess, it might be a bad switch. Nope. The switch, when disconnected, works fine - open when depressed, closed when extended. I found the wire from the switch to the bulb (negative/ground, brown/black) was continuous to ground even when disconnected from the switch.

    The switch is used to connect the bulb to ground when the lid is open. I found that the wire from the switch to the light has a tee tap – another black wire leading back alongside the positive RD/GN wire. I cut that and found that that tee tapped wire is grounded, thus completing the circuit regardless of whether the switch is open or closed.

    That wire is NOT shown on any BMW E30 325ix drawings. (I have the official 1989 BMW 325ix Electrical Troubleshooting Manual). The 5th and 6th pictures in the original post of the DIY thread show the tee tap. http://www.r3vlimited.com/board/showthread.php?t=172160

    (I tried adding my own picture showing the extra tee tapped wire but could not a Google Photo to link properly.)

    Another way to ask the questions is: What other component or system needs to know when the trunk lid is open or closed? That is what that extra, tee tapped wire is doing – going negative/ground when the lid is open and going open when the lid is closed. Or, at least that is what I would expect it was added for. I need to know where it goes so that I find why it is now permanently grounded.

    The type of connection makes me think it might be an after-market add-on. Mine was a bare wire spice covered with tape. The one in the DIY thread shows a crimp connector.
    Photo with labels

    Oldsnowman

    #2
    Do you have an aftermarket alarm on the car? One was likely installed at some point. There's no other reason to tap into the trunk light circuit that I can think of other than a 2nd trunk light of course.

    Other thoughts... the trunk light will also stay on if the trunk latch is adjusted loose enough for the switch not to open. Also if that is an alarm wire, it should be diode isolated to prevent the light from turning on with the interior dome lights.
    "I'd probably take the E30 M3 in this case just because I love that little car, and how tanky that inline 6 is." - thecj

    85 323i M TECH 1 S52 - ALPINEWEISS/SCHWARZE
    88 M3 - LACHSSILBER/SCHWARZE
    89 M3 - ALPINEWEISS II/M TECH CLOTH-ALCANTARA
    91 M TECHNIC CABRIO TURBO - MACAOBLAU/M TECH CLOTH-LEATHER

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      #3
      Originally posted by reelizmpro View Post
      Do you have an aftermarket alarm on the car? One was likely installed at some point. There's no other reason to tap into the trunk light circuit that I can think of other than a 2nd trunk light of course.

      Other thoughts... the trunk light will also stay on if the trunk latch is adjusted loose enough for the switch not to open. Also if that is an alarm wire, it should be diode isolated to prevent the light from turning on with the interior dome lights.
      I do have an aftermarket alarm. I'll have to try a few things to see if it is related. Thanks.
      Oldsnowman

      Comment


        #4
        Is it an old alarm installation? it could be the wiring is shorted to ground inadvertently on the way to the brain. If this is the case, then when you arm the alarm it should beep 3 or 4 times to let you know a door is still open because it sees the trunk as a door that's still open. Time to start troubleshooting...
        "I'd probably take the E30 M3 in this case just because I love that little car, and how tanky that inline 6 is." - thecj

        85 323i M TECH 1 S52 - ALPINEWEISS/SCHWARZE
        88 M3 - LACHSSILBER/SCHWARZE
        89 M3 - ALPINEWEISS II/M TECH CLOTH-ALCANTARA
        91 M TECHNIC CABRIO TURBO - MACAOBLAU/M TECH CLOTH-LEATHER

        Comment

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