[Vwdiesel] more alternator questions

[Sandy Cameron]

At 12:21 AM 01/08/2006 -0700, you wrote:>


>Now, here's where it gets strange: during all of this, the amp light
>never came on to tell me that it was not charging (which it definitely
>wasn't--if I charge the battery up, start the car, and check the
>voltage at the battery now, it's about 9.8v). In fact, the amp light
>NEVER comes on, even with the key on but the engine not running. I

Sitting for a year in the weeds, hmmm (stroking beard),

 I would recommend opening the alternator, or, if the brush holder will come
out without dismantling, do it on the car. Check for stuck brushes, and the
pressure spring connection to the alternator innards from the brush holder
(if it is removable)

Manny critters love to live inside things like alternators, and drag in
assorted flora to make themselves comfortable. Also a year's inacitvity can
result in problems with corrosion of internal connections.

The bottom line, since the bulb lights when you ground the field excitation
wire, you KNOW it's related to field excitation when it does NOT light when
properly connected.

The bulb circuit is 12 volts looking for ground through the regulator, and
ultimately the brushes and field (one brush is grounded, and the other is
fed from the bulb initially, then the diode trio inside the alternator once
running.  

The diode trio is NOT related to the 6 alternator rectifier diodes, but is a
group of 3 lower rated diodes that just supply field current when the
alternator gets fired up.
They are however, connected to the same 3 wires the main diodes are connected to

The problem is most likely related to the brushes,
less likely related to the regulator, , but check all the connections at the
regulator and alternator related to the field

The field is not drawing the current it should when the key is turned on.

Sandy