The warning light acts like a set of balance scales between the alternator
field voltage and the car system voltage. If they get out of balance (i.e.
different voltages) the lamp lights, if they are in balance (i.e. same
voltage) it doesn't light.
The light should come on when you turn the ignition on, then when you start
the engine and increase the revs above about 900rpm it should go out. It
should then stay out unless either:
1. The revs drop below about 600rpm - at which point it will come on full
brightness and remain so until the engine is revved above 900rpm again, or
2. You switch off the engine. With the ignition off but the engine still
spinning the lamp will light, then dim out as the engine comes to a halt.
There are slight differences between dynamo and alternator equipped cars,
but not much.
If the light does not go off when the engine is revved, or suddenly comes on
full brightness, the implication is that you have lost the charge. This can
be confirmed by measuring the voltage on a brown wire at fast-idle. You
should see about 13v to 14v if the system is charging correctly, you may
only see 12v if it is not.
If the light glows dimly at night, and the brightness increases as the
electrical load is increased, the implication is that one or more of the
diodes in the alternator have failed. You will get different combinations
of incorrect noise, heat and/or voltage depending on which diode(s) have
failed and whether they have gone short or open. It is possible that the
alternator appears to be giving the correct output voltage even though the
light is glowing, but you may find that it has a reduced current capacity on
full load.
A bad connection in the warning light circuitry itself is unlikely to cause
the lamp to glow, it is more likely a problem in the charging circuit, or
possibly a bad connection in the brown - ignition switch - white - coil
circuit.
PaulH.
----- Original Message -----
From: <KD6BGO@aol.com>
To: <mgs@autox.team.net>
Sent: Friday, December 22, 2000 6:07 AM
Subject: Next question: that darn ignition warning lite!!
> Next question: ignition warning lite circuit. I noticed tonite after
driving
> the car for about an hour, the lite started to glow. Headlites were still
> good and brite, blinkers still flashed at the same rate. I suspect that
maybe
> I have a loose or corroded connection in the warning lite circuit itself.
Can
> anyone explain the warning lite circuit to me? Any suggestions where to
start
> looking?
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