Alternator Question

Mark R speedracer.mark at
Mon Dec 10 13:02:59 PST 2007

You know the alternator is good (can output 14V at load), so if you're
having a voltage drop, the issue is in your primary wiring.

The only other situation that can mimic the conditions is a dead-short
inside the battery (across one of the plates), but you'd be unlikely to see
12V when "fully charged."  Of course, a free battery test will rule that

As for continuity, what you described was a test for amperage, not
continuity (which is the OHMs scale, not milliamp scale).  Might want to
confirm or scan in the bentley pages and I'll write you a procedure.

Bad primary wiring is common with older VAG products.  Primary wiring I'm
talking about it battery to starter, starter to alternator, fusible links...
basically anything large diameter under the hood.

Quick test:
Hook up voltmeter across battery.
Voltage: (should be about 12.5 volts)
Start car.  Idle Voltage:  (should be higher, about 14V)
Put a load on the alternator (fans, high beams, etc.)  Voltage (should be
the same as above).

Hope I've helped more,
Mark Rosenkrantz

On Dec 9, 2007 2:25 PM, Vittorio Bares <Vittorio.Bares at> wrote:

> Back at it - I've replaced the alternator w/a refurbished one - I now
> have 2 fully working units (tested at AutoZone) :\.
> Went back an cleaned contacts behind the snub nose (alternator bracket).
> Cleaned contacts to adjustment bracket.
> Voltage is dropping when revving the motor.
> The diagnostic display for voltage on the climates control remains at
> 12.0 (channel 11). This is regardless of what the needle on the gauge is
> doing. It used to properly indicate the voltage.
> Needle shows just over 12v on idle. Verified w/volt meter.
> Voltage off of the alternator (+ post to engine ground) is about 12.5v
> (seems low). I presume (it has a 14v regulator) it should read 14v from
> somewhere - anyone know where to measure that from?
> Anyone know how to check continuity of exciter wire (blue) from
> alternator? Bentley says to check current across wire to alternator
> exciter post - I set my multi-meter to DC 250ma and the needle shot over
> max (?) Bentley says it should be between 150-180ma - indicates if its
> low to replace climate control board - doesn't say anything if its above
> ?
> Steve suggests in the attached thread to check voltage from the battery
> - since the battery is charged via ground (I believe), would one try to
> directly from one of the alternator mounting brackets to the negative
> post on the battery (a direct ground)?
> BTW - this is on a 1990 Audi 200 avant.
> Thanks!
> Vittorio -
> -----Original Message-----
> From: quattro-bounces at [mailto:quattro-bounces at]
> On Behalf Of Mark R
> Sent: Monday, September 24, 2007 1:36 PM
> To: Steve Sears
> Cc: quattro at
> Subject: Re: Alternator Question
> Steve's got it right... often overlooked is the primary wiring.  Audi
> didn't use the greatest wiring when new, and now you'll often find
> corrosion under the sheath due to moisture wicking.  Remember, the
> alternator has to have the ability to get the current (amperage) out as
> well.
> Another quick and dirty test is to check voltage at the battery versus
> the alternator post (if available when engine is running).  Set up the
> wiring before starting the engine.  If you see a voltage change (drop
> along the wiring), you'll need some attention there.
> Cheers!
> Mark Rosenkrantz
> On 9/24/07, Steve Sears <steve.sears at> wrote:
> >
> > Vittorio,
> > If the alternator is one of those 110 amp units, then the two bolt
> > pivot is correct.  If it is the 90 amp unit, then it should have a
> > long bolt and nut at the pivot.  If you were to hook a long jumper
> > cable directly between the snubber mount to the battery ground, would
> > you get a different reading?
> > (The engine ground to chassis across one of the engine mounts may be
> bad).
> > You might also check the condition of the battery cable splice.
> > Cheers!
> > Steve Sears
> > 1962 and '64 Auto Union DKW Junior deLuxes 1980 Audi 5000
> > 1987 Audi 5000 Turbo Quattro
> >
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