On Mon, 23 Apr 2007 23:10:35 GMT, "Carl Ijames"
wrote:

On these alternators the dash volts light is a 194 and it
goes from battery to the L pin on the 4 pin connector, to provide both
sensing input and idiot light. The internal resistance of this bulb is
crucial, you will blow things up if it is shorted and make things very
unhappy if it is open.

The idiot light supplies the current to magnetize the field until the
alternator is producing power. The light goes from the positive of
the ignition circuit to the field. There's an additional set of three
positive diodes on the alternator that also go to the field - when the
alternator is producing its own power, the light bulb has positive
voltage on both terminals and doesn't light.

Good design to use the alternator itself to supply the field through
isolation diodes - a shorted rotor won't output enough current to
destroy the regulator that way.

Short the lamp and you may destroy the regulator or rotor or both -
too high a lamp resistance and it will change the point where the
alternator begins charging or keep it from charging.

The lamp serves two purposes - tells you the alternator is working and
supplies current to the field to start the alternator working.
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