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    Wiring Chaos

    I bought the car this past april. Fuse 21 burned out about two months later, replaced it and it worked fine for about two months, and then one, and then two weeks, and then a week, and now when I replace it, it will work only if I don't turn the engine on.


    I can replace it and listen to the radio on acc but as soon as I push the clutch in and turn the key all the way and the engine comes to life (to see the tachometer work, which is part of fuse 21's circuit) , the damn fuse blows. ALTHOUGH, twice it has happened, that while troubleshooting in the afternoon the fuse will work even when I turn the engine on. I turned it on and off over 5 times and I was convinced that whatever wire was causing the blown fuse, I'd covered it or isolated it properly. I even made a point to drive it around the second time it happened to make sure it wasn't a fluke.


    the problem was, the next morning, on both occasions, I got in my car to go to class and the problem would be there like the day before had never happened.


    now here is where my excellent DUMBASSNESS comes in! On the third time, (after those two happenings) that I was also convinced I'd fixed it, I was smiling and putting everything back the way it went when I confused the defrost button and its respective plug. I plugged it in, and pressed it to see the little yellow button light up when the dashboard lights turned off.


    When this happened it all turned into a blur. I quickly remembered that there was a third plug back there that did not have a button assigned to it and just sat back there alone. That's what I most likely was holding in my hand with the defrost button plugged in to it

    ...and this is why I'm here humbly asking for your advice.


    did my mistake cause this? (pretty sure that's a yes)


    SYMPTOMS :
    Before the dashboard and obc backlight lights completely died they did something weird. When the headlight knob was pushed all the way in or halfway (I can't seem to remember) the dashboard and obc backlight lights would work great, but when I pulled it all the way out to turn on the headlights they would turn off. Since I could go back and forth between the headlights and dashboard/obc lights I figured I'd just connected the wrong wires. When I tried to fix my problem I found out that the lights would not come on at all anymore.


    In addition to this, my turn signal stalk will not work. I don't know if this is somehow connected to all of this or if it's just a new problem. (my hazard lights will turn on if I press the button so I know it has something to do with the stalk itself)


    So I guess this is a fuse 21 problem along with a dashboard/obc lighting problem. The bentley wiring diagrams show no real full circuit routes for fuse 21 (hopefully i'm wrong and you guys prove me wrong with a page number of the page that i'm skipping)


    I found the wire that provides lighting for the obc backlight but, again, the bentley just says something like "wire coming from dashboard lights" and I can't find this end of it in another diagram.


    CLIFF NOTES:
    >fuse 21 and dashboard/obc lighting acting screwy.
    >fuse 21 works fine until the engine turns on.
    >need extra information on what extra circuits come into play with fuse 21 when engine turns on and how the dashboard and obc light wiring is set up.


    PLEASE include in your response at least one insult and one suggestion, then whatever else you'd like (perhaps a fail picture reference or a diagram for wiring retards like me).
    09/1989 325i 4 Door
    +M30 Swap
    +Z3 Steering Rack

    #2
    Fuse 21 supplies power to a number of things, but the only ones that strikes me as being related to the engine being running is the tach/econometer and part of the injection electronics. The first thing I'd try would be to disconnect the cluster and see if the fuse blows when the engine starts. If it does something else besides the tach/econometer is the cause.

    The dash and OBC light problem may be related, or may be due to a different problem.

    I think you'll have better luck in solving this by using the factory wiring diagrams, which you can get from http://wedophones.com/BMWManualsLead.htm
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

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      #3
      well gave up after two or three weeks of trying and school going on at the same time... by the time finals came around i just gave up and sent it to the mechanic.

      Turned out it was the starter motor shorting through the harness and jumping unto fuse 21 wiring as I understood it from him.

      When I pulled my act of stupidity I most likely shorted the headlight knob switch, which had to be replaced.

      Those were the only problems causing the short and dimmer switch problems.
      09/1989 325i 4 Door
      +M30 Swap
      +Z3 Steering Rack

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