In a Vanagon the dash alt light led current itself does not provide the
excitation but there is a 150 ohm resistor in parallel with the alt led
that does provide a small initial startup current to trigger the
alternator field winding.

Mark

Tom Hargrave wrote:
> ..............
>
> But a alternator rotor retains so little magnetism that it usually takes a
> small amount of current to start one up. That initial current is supplied
> through your GEN dash light. Then, once the alternator starts up a smaller
> of two diode bridges inside the alternator provides current to the
> regulator. The larger diode bridge provides current to the car's electrical
> system.
>
> BTW, this is why your GEN light stays on when your alternator or regulator
> fails. The alternator rotor is no longer receiving excite current from the
> regulator and it continues to draw the small amount of current through your
> GEN light. But the current is not enough to drive the alternator to put out
> any real power.
>
>