At 09:55 PM 6/28/01 -0500, D T Gebhard wrote:
>Spitlisters:
> What causes the ign. light to glow and glow
>brighter as I accelerate. I have a bosch
>aftermarket alt. with an output of 14.5 volts.
>Battery was new in May. Where do I look first.
> Thanks
> Dave Gebhard
I didn't see anyone reply to this earlier so I'll have a go at it and
apologize if someone else has already covered this.
The ignition light on our Spitfires is really completely unrelated to the
ignition system outside of telling you that the key is in the ignition
position. It's real function is a generator/alternator warning light.
Turn the key, the light comes on full. Rev up the engine and the light
goes out while you are charging. If the light glows brighter the faster
the engine is running, then it means that the wire from the
generator/alternator to the warning light is getting closer to ground
potential. Normally with the engine off this wire is connected to the
ground through the generator/alternator's windings. Once the engine
starts, this wire goes to 12 volts on one side of the warning light versus
12 volts on the other side connected to the battery. With both wires at 12
volts, the bulb does not light and things are fine. When the bulb starts
glowing, it means that the wire from the bulb to the generator/alternator
is starting to be lower than 12 volts and getting closer and closer to
being grounded through the generator/alternator. This indicates a problem
with the voltage regulator usually.
You can test this by disconnecting this warning light and shorting it
directly to the chassis. On early models it will be a small brown wire
with a green stripe at the generator. Short that to ground. If you have
an alternator, the wire will be a small brown wire with yellow stripe.
Again, short it to ground. This should cause the light to glow full
intensity with the key on. Start the car and it shouldn't change (stay
lit). This will tell you the warning circuit is fine, but the charging
circuit is not.
The longer you drive this car, the sooner the battery will die from not
being charged. Most of the time charging units die and don't charge on the
lower end of the RPM range, but upper limiters can have problems too.
Since you have an aftermarket alternator, I don't know if you have an
internal or external regulator. That's the first thing to check. The unit
does spin up to 14.5 volts at idle. That means the alternator itself is
capable of charging (you need at least 12.6 vdc to charge, preferably 14-16
vdc with 14.8 vdc ideal), but the regulator starts cutting the charging
circuit out at higher RPMS. It is a voltage regulator problem. If the
regulator is built into the alternator, then replace the entire thing. If
not, replace just the regulator.
Vegaman Dan
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