Alternator Question

Vittorio Bares Vittorio.Bares at
Sun Dec 9 14:28:36 PST 2007

More diagnosis:

Leaving it at idle for a while seems to bring the (system) voltage back
to the point where the gauge shows 14v (volt meter never shows more than

Cooling fan, or headlights instantly bring the voltage down below 12v.
Smaller accessories such as dome lights, blower or dash lights don't
have much of an effect.

Tried using booster cables to ground the radiator fan to the motor. No

Engine revs have no effect on voltage once the system gets above 12.5v.
Took the car for a test run - went well enough for a while - voltage
dipped a little when fan came on - but not bad. Then I tried the lights,
ok for a short spell, then the fan came on and basically killed the
system. Charging well below 10v, car started running badly (not as much
power, lightly missing) - looks like I was running on battery only (?)
and the extra juice from the lights on and the fan on sucked too much
out of it.

Made it back home - let it idle for a while, gradually the volt meter
made it back into the normal range, around 14v.

Right now, it would appear that the lights and the fan are running an
unusually high load - what does that actually mean in practical terms -
what am I looking for?


Vittorio -

-----Original Message-----
From: Grant Lenahan [mailto:glenahan at] 
Sent: Sunday, December 09, 2007 2:50 PM
To: Vittorio Bares
Cc: Mark R; Steve Sears; quattro at
Subject: Re: Alternator Question

I'm not sure where to start, and excuse me if you know all this, but a
few comments and questions come to mind:

1. You say it shows 12.5V running at idle.  It should be 14+V. This
suggests the voltage is too low, preventing the regulator from working.

2. You also say it is dropping when revving the motor. Is this correct?
Current - and thus ability to maintain voltage across any given load -
should rise with RPMs.  Yet it is falling. The only explanation I can
think of is that the load is rising - faster than the rpms.  So what
draws power more at high rpms?  Under normal operating conditions,
nothign I can think of.

So this is a long-winded prep to "stop trying to fix the alternator and
go find the unusually high load".

Or, of course, find out if something is current limiting the alternator,
which might look similar.

3. If the diagnostic display now reads 12v - regardless of actual
voltage - it suggests that something is amiss in he dash cluster.

4. Could these be related? Or might the dash cluster simply be
inaccurate when working from a B+ voltage that is out of range. I dont
know, but I've seen that in the past. Way int he past.

Good luck in your quest.

On Dec 9, 2007, at 2:25 PM, Vittorio Bares 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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