Conference terri::cars_uk

    I had a new problem with my car (Alfa) last night and wondered if anyone
    has a good idea of what went wrong...
    
    Basically, when I turn the ignition key OFF, the battery warning light
    comes ON.  When I turn the key to the ON position, the light goes OFF.
    
    The engine starts normally, with the warning light not showing until
    the key is turned to the fully off position...
    
    Recent background :
    
    I had a problem recently where the power did not always go on when
    the key was turned on, but a liberal dousing of WD40 into the lock
    seemed to fix that.
    
    One other point, the engine did cut out yesterday on a roundabout.
    When I checked later, the battery lead was loose, so I do wonder
    if there could have been some alternator damage (the engine only
    cut out temporarily, then continued).
    
    
    Anyway, I guessed that this new problem was caused by the lock.
    Simple check is to disconnect the multiplug connectors coming
    from the ignition switch.  Guess what ?  The light stays on !
    
    Of course, having this warning light on overnight managed to drain
    my battery.  I jump-started the car this morning and have disconnected
    the battery lead whilst the car is parked at work.
    
    Note that the petrol/temp gauges do 'switch off' when the key is
    turned off, and read normally when key is turned on again, so it
    isn't a case of the whole system being live all the time.
    
    
    So, does anyone have any specific suggestions as to what is wrong ?
    
    J.R.

    re .2
    
    The warning light normally supplies power to the alternator to turn it
    on when the ignition is turned on.  It lights up if the alternator
    is not generating enough electricity to provide its own internal power
    requirements. If the light comes on when the ignition is off it must be
    because current is flowing the other way I.e. from the alternator via
    the light to ground. This is almost certainly because the alternators
    electronics are bad - most likely one or more of the diodes are bad,
    allowing current to flow from the battery to the internals of the
    alternator.
    
    Andrew

	
	This is a different, but related question.  Could a lose
	earth on one side of the ignition light cause it to come
	on?  Maybe what I need is an understanable wiring diagram.
	But as I understand it, the alternator has two wires coming
	out of it (the modern, alternater + regulator does, anyway).
	One goes to the battery (live) and the other, smaller one,
	goes to the ignition warning light (via a fuse).  I recently
	had a problem with that fuse, shared by my water temp and
	fuel gauge.  There was oxidation around the contact and
 	this caused my ignition warning light to come on - how?
	(And the gauges to read low).

	Dave

    Re: .4
    
    If the diagnosis is that you have suffered diode damage doesn't this
    mean you may get away with just replacing the regulator ?
    
    Steve.

    re .5
    
    A bad contact where you describe could make the alternator supply
    current via the warning light to the gauges. If the contact was
    non-existant your gauges probably would not move, nor would the light
    come on (and your battery would die ...). A high resistance contact
    would allow sufficient current to pass to make the alternator work, but
    not enough to keep the gauges happy.
    
    re .6, .7
    
    In some alternators you can replace just the diodes (They are a common
    failure point). In some others you may have to replace all the
    electronics. If you're really unlucky you might have to replace the
    whole thing (especially if your garage has a spare alternator, but not
    the parts !)
    
    Andrew