Ignition Light ???

[HAN8L1965]

Tell me about the function of the ignition light. On the 65 when I first turn it on it glows brightly then as the car speeds up it dims to going out is this correct. What exactly is it's function, what is it telling you? I know I read in another thread that if the bulb were not in place or burned out the car would not start.

So many questions, but it sure is fun.

Mark

 

[Trevor Jessie]

If your car has a generator, then it is telling you the generator/control bo is not charging the battery. Once it goes out then you know the generator/control box is charging the battery. If the bulb burns out it will not affect the operation of the car.

 

[HAN8L1965]

Thank you Trevor, yes my car does have a generator and the bulb does go out so that is telling me the generator is working and charging the battery.

Mark

 

[DrEntropy]

And if it comes ON when you switch the iggy OFF, the brushes in the genny need replacing. :wink:

 

[jlaird]

Oh, good tip Doc.

 

[zimmy]

mine goes off when i start the car...
its kinda like a voltage sensor,
if the voltage isnt correct, the
light will shine.....
theres a more technical explanation
but ive just woke up :wink: .....zimmmy

 

[GeeBee1]

Zimmy

More like an amp-meter.

 

[Sarastro]

OK gang, lemme see if I can clarify this a bit.

The "ignition" light (really a serious misnomer) is connected between the battery and the generator output when the ign switch is turned on. The generator output is zero, so the light comes on.

As the engine starts and the generator output increases, the voltage across the light decreases and when the generator is within about 4-5 volts of the battery voltage, the light goes out. So, in essence, it's a crude indicator of whether the generator is working, more or less. If the generator output is zilch, it will come on when the car is running; if the generator is putting out anything over maybe 8 volts, it will go off.

The light really tells you nothing about whether the generator is charging the battery, or whether the battery is charging or discharging. You can turn on all your lights at idle, and I can guarantee that the battery isn't charging--there is more current coming out of the battery than the generator can provide, so the battery is discharging. Even then, however, the ignition light will be off, because the poor, suffering generator is still putting out the right voltage. Just not enough current to meet the demands of the car's electrical system.

Finally, unless I'm missing something, I have a hard time seeing how the light could stay on after the ignition is switched off--in the bugeye, at least, it is completely disconnected from any source of power when you turn off the switch. Maybe in later cars, the situation is more complicated? I dunno. I have a bugeye.

On the other hand, if the light stays OFF when you turn the ignition switch ON (and you know that the bulb is OK, of course), that could be an indication that the generator is open-circuited, which could be caused by bad brushes. In this case, the light will stay off when the engine is running, too, but the battery will definitely NOT be charging.

 

[DrEntropy]

Finally, unless I'm missing something, I have a hard time seeing how the light could stay on after the ignition is switched off--in the bugeye, at least, it is completely disconnected from any source of power when you turn off the switch. Maybe in later cars, the situation is more complicated? I dunno. I have a bugeye.

With a voltage regulator in a bakelite container. When the copper wire(s) attached to the brushes makes full contact with the commutator (a "dead short"), the contacts in the V.R. slam shut and the light comes on... matter of fact, turning the key back on will cause the light to go OUT.

~IF~ this ever happens, may I suggest the battery should be disconnected post haste... or you'll be replacing both generator and the regulator. Possibly some harness bits as well. First time I saw this I was so "fascinated" I allowed it to remain and witnessed the smoke escape from the regulator. Lesson learned. I only posted it for warning purposes.