200 charging issues (was:instrument cluster lights)

Keith Lawyer wbr90 at yahoo.com
Sun Dec 22 20:47:47 EST 2002

--- Dave C <conner at cfm.Ohio-State.edu> wrote:
> You need a multimeter (MM) and begin learning how to
> use it.  It would have a setting to test continuity.

Yes, I feel like a complete moron!  That should have
been painfully simple to me, why I did not think of it
I will not know.

> I believe it is perfectly harmless to start and
> drive the car without the
> instrument cluster installed.

Good to know.
> You say the system is not charging... but how do you
> know?  What are the symptoms?

It all started when my gf was driving to work and the
car began acting odd, bucking, auto-check batt
indicator came.  She checked her gauges and saw the
voltage was extremely low (lack of accuracy of the
stock voltmeter aside).  She turned off all
accessories (blower motor, rear defrost) and limped it
to work.

I pulled the back seat and jammed my multimeter (see I
do have one, just too stupid to figure out to use it
to test bulbs even tho I test fuses and sensors with
it all the time) leads into the batt terminals.  On
Saturday I ran into town with ALL possible accessories
on, including high beams and heated seats, and it
charged happily at 13.5-13.6 (which IME equates to at
least 13.8 at the jumper post given the resistance in
the stock pos batt cable).

Later in the day I started it again and was only
seeing 11.9 or so at the batt, slightly more at the
jumper post.  Considering the battery will happily
hold 12.8 (I charged it) the alt is obviously doing
nothing.  It was at this time I looked for the alt
warning lite and noticed it was not lighting (BTDT on
other Audis).

I was *once* able to get the alt to start charging by
revving to 3500 rpm, verified by a quick jump on my
multimeter to approx 14.1, but then it would not
continue charging.  Now, no degree of engine speed
will energize the alt.

I'm willing to concede the alt could be bad, but this
still would not explain why the alt lite is not
working?  As I said, the exciter wire is grounding
when the vehicle is not running, at least as far as
the connector by the jumper post.  This should provide
the ground the bulb needs, while the ign switch
provides the 12V, no?

Clearly more investigation is warranted, but given
that I see no corrosion I'm not certain what would
make the alt lite _suddenly_ just stop coming on when
the bulb is good.

Perhaps a bad printed circuit as Huw suggested?

Keith L
still confused

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