On 2/26/05 22:14, "Phil Krueger" <vwuprising@YAHOO.COM> wrote:

> I am completely stumped with an alternator light
> problem.  The idiot light stays weakly lit constantly
> and I can't find a short anywhere.  The alternator is
> new and kept the light out temporarily but began to
> weakly light again.  Does anyone know how the Bosch
> voltage sensing system in the alternator works and is
> it prone to isolated failure?  I suspect that faulty
> wiring somewhere caused the failure of the sensing
> circuitry and now the alternator has a voltage output
> of higher than the battery and creates 2 different
> potentials across the idiot light. I have ruled out
> the starter and refer as short suspects.  Could a
> short in the battery cause this?
> 
> Thanks

Is this a pax van or a camper? If it is a camper there are several
possibilities.

If you added an aux battery there is also another possibility related to the
camper stuff as well.

Basically the light works on kirschoffs law.  If voltages are equal to both
sides of the bulb the light is out.  I.e. The regulated voltage out of the
alternator to the battery is at 13.5 and the voltage at the battery is at
13.5 the light is out.  When alternator is not putting out then the alt out
is 0 and the battery is 12.5 so the light is on. Various camper or aux
battery related relays can be disconnected to isolate the problem. Also
check the connection of the light wire on the alternator to make sure it is
solid.
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jimt
Planned insanity is best.
Remember that sanity is optional.
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