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Re: Alternator or ? fails

> From: donohue@azstarnet.com (Terry Donohue)
> Date: Mon, 13 May 1996 11:34:39 -0600
> Subject: Alternator or ? fails
>     We just moved to Tucson, and I drove the family on the very scenic
> mountain road to the top of Mt. Lemmon (9000 ft).  Unfortunately, the
> charging system in my '90 200 TQ quit right at the top.  The indications
> are:  Alternator warning light on, as well as the "Antilock Off" and brake
> warning lights on.  The voltmeter initially read about 12V.  I decided to
> see how far I could get running off the battery (fortunately new as of last
> fall); I made it within a few miles of home (45 minutes of driving!; the AC
> was off, and the outside temp. was 105), and AAA got me the rest of the
> way.  Other useful info:  The car will run until the voltage drops to
> slightly below 10V.
>      The Bentley Manuals are not very helpful, in fact, downright obscure
> when it comes to charging problems.  Anybody have an idea on the most
> likely culprit?  Bad wire; bad voltage regulator; bad alternator; or else?
> Also could use recommendations on sources for used alternators, if that is
> the way to go.  TIA.
> Terry Donohue
> donohue@azstarnet.com
> '71 BMW 2002Ti
> '90 200 TQ
> '95 BMW M3

I would fully charge the battery, then start the car. Before you do it, turn the
iginition on, place the climate control to monitor voltage (hit outside
temperature and off at same time, hit warmer up to channel 11, then hit outside
temperature again). Record battery voltage. Start the car and note the change.
If no increase in voltage, take the back cover off of the alternator (black
piece) and using a voltmeter, measure voltage at terminal of small and large
wire. Both should have battery voltage on them. If there is no voltage,
determine where there is an open circuit. If both have battery voltage, I would
suspect the alternator.

Take it out and bring it to a local automotive electric shop, they can
troubleshoot/repair it. If it is brushes, regulator, diodes or other simple
problem, it will probably take less than a day and $75 to fix it.

Paul Waterloo
Colchester, CT

87 5KSQ