It sounds to me like the stereo guys tapped the blue field wire as an "ignition on" source. I've seen it happen a few times before. If that wires messed with, no charge. 
I believe, but someone please check me on this....
You could jump 12v to the blue wire on the alternator straight from the alternator stud and see I now your charging. That should work....I think. 

-craig
"87 sunroof Syncro westy zetec
"90gl
"85 residence

On Oct 4, 2012, at 7:28 PM, Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM> wrote:

> If you have another regulator/brush package ..
> no harm in seeing what happens by trying that one.
> 
> I find that 'most' waterboxers either take no rev to get charging started,
> or just a slight one.
> I find that on an 82 DV with 65 amp alternator ..it takes quite a good
> rev to get it to start charging.
> 
> If you really man that the warning light is off, but by voltage
> measurement charging has not started ..
> that's rather weird.  Doesn't make sense really.
>   If that is happening I'd sure try another voltage regulator.
> 
> what voltage to you have now ?
> I like to see 13.8 min ....and it can keep up to that with headlights on
> too.  Or more, up to 14.5.
> There is such a thing as a solid state adjustable voltage regulator too.
> 
> scott
> turbovans
> 
> On 10/4/2012 4:20 PM, HotelWestfalia wrote:
>> Thanks to all who responded.
>> 
>> I have to rev up the engine quite a bit to have the charging start, even though the charging light is off.  Perhaps the voltage regulator is not kicking in as early as in other cars.
>> 
>> Scott mentioned, sometimes it may need to be revved up to get the charging to start.
>> 
>> Thank again,
>> Zoltan
>> 
>> From: Scott Daniel - Turbovans
>> Sent: Wednesday, October 03, 2012 11:49 PM
>> To: HotelWestfalia
>> Cc: vanagon@GERRY.VANAGON.COM
>> Subject: Re: Baffled, giving up
>> 
>> What's the status of the blue wire to the alternator ?
>> is the instrument cluster  installed ?
>> Does the warning light come on when you turn on the key ?
>> The alternator won't 'wake up' until it's excited by the blue wire connection.
>> 
>> 
>> 
>> On 10/3/2012 11:10 PM, HotelWestfalia wrote:
>> 
>> Hi to all,
>> 
>> I was working on the charging of the alternator, because I found the charging being too low.  Took the alt. out and took it to the store for checking.  It passed with almost 14 volts.  Great.  I put it back in the car and got 11.98 volts at the battery, at the alt. same.  Shut the car down and the battery is back to 12.4 volts.
>> 
>> I can’t think of anything that I can look at.  The only thing happened in the near past is that a radio was installed by a shop.
>> 
>> Anyone?
>> 
>> Zoltan
>> 
>> 
>> 
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 2012.0.2221 / Virus Database: 2441/5308 - Release Date: 10/03/12
>>