1999 E46 318i battery light wiring/source?

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  1. 1999 E46 318i battery light wiring/source? 
    #1
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    BrianD's Car Details
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    Hi, I have a 318i, the earlier M43 engine. When the ignition is switched on, the oil pressure light and usual warning lights come on, but not the main ignition/battery warning light. Always been like this in my ownership, I assumed a bulb gone and ignored it. The car is definitely charging and everything works Ok with no other electrical problems that I know of.

    Until I switch the rear screen demister on, then the main battery warning light comes on. Two part question really - what is the source for the battery light when the ignition is switched on, any clues on fixing this? Second - any ideas why the light comes on with the demister?

    I believe that the car is still charging with the demister on, but never tried leaving it switched on just in case. Thanks for any ideas or links to a wiring diagram.

    Brian
     
     

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    #2
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    ako89's Car Details
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    Sounds to me like a buggered earth wire. As for the battery light, I believe it only comes on when your not getting enough power from the alternator. #

    what I'd try is switching everything else on at once, use as much power as possible. Bar the demister.

    Then again, it should come on when you first turn the key... =/

    Does sound like a bad earth, have you tried the manuals? Haynes/Bentley etc
     
     

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    Thanks for the reply. An earth wire to/from where were you thinking of? (To earth ha ha). Definitely not the battery light coming on in the normal sense, ie when the alternator is overloaded and not charging, as it will happily run everything else (lights heater etc) all wound up to eleven on tickover without even a slight glow from the red warning light, but the screen demister just acts like an on/off switch for the battery warning light. Not coming on initially when I switch the car on is also a mystery. Don't have a manual for the car, off to ebay/amazon now .....

    Cheers
    Brian
     
     

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    Haynes manual ordered online, hopefully will have wiring diagrams in there to help me trace it. Does anybody know where the red battery light gets the power from when you turn the ignition on, ie what should make it light up?
     
     

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    The warning light comes directly from the alternator. Sounds to my like the rectifier in your alternator is faulty not the wiring.
     
     

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    Thanks, would there be any other symptoms from a faulty rectifier? Sorry, no idea about electronics/electrics. The car has been driving fine like this for a month (since I bought it), only noticed the battery light issue the other day when I switched the rear demister on for the first time.

    Cheers
    Brian
     
     

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    #7
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    To revive an old thread as things have changed ...

    The engine bottom end sounded a bit ropey so I swapped for a low miles recently reconned engine complete with all anciliaries including alternator already bolted on. When I switched the ignition on for the first time - fantastic, I now have a battery warning light with the ignition. However when I start the car I still have a battery warning light on. Pretty sure that the new alternator is charging Ok and that there is some odd issue in the wiring somewhere that was previously "cured" by an engine loom bodge that stopped the light coming on. So the question this time round, when everything is working properly what is it that makes the light go out when the engine is running? The new engine alternator etc came with full engine harness connected up that I've used rather than changing for the old engine loom.
     
     

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    #8
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    Sorted from info on an old post I missed when searching first time round, fuse 30 blown by faulty oil level sensor on the old engine, when fuse 30 is blown red light stays on.
     
     

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    Good one on getting it sorted.
    THat fuse may also have been causing some of the problems to begin with.
    Glad its sorted
     
     

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