alternator indicator light hook up

[seasanford]

Hi All,

All my wiring is in place and working, except for a couple of gauge indications. I'm using the doner car wiring. One problem I have is the alternator indicator light.
The alternator is new and charging. The Battery is also new. When the car is running I can disconnect the battery and the car keeps running. The problem is that the alternator indicator light is always on. I read that this light is fed power from the alternator and also from the battery...this has me very confused.
Does anyone have a simple diagram of how this would be done?

Thanks,
R. Pace

[xatudor]

I don't have a diagram, but I'll try to explain. One wire goes to the battery (via ignition switch)and will be at 12V, the other goes to the alternator. When the alternator is not spinning and/or not charging, that wire will have a voltage less then 12V. The difference in voltage between the two will cause the lamp to light up, the larger the difference the brighter the lamp. Also some of the alternators use this wire to start the charging (excite the field) when the engine is first started.
Hope this helps.

[seasanford]

Pardon my thick skull.
When you say one wire goes to the battery via the ignition switch, is this wire from the alternator indicator light? And the other wire going to the alternator, is this the other wire from the alternator indicator light?
So in my head I see no actual ground, just voltage from each direction pushing against eachother. (no flow). Is my reasoning on the right track?

[xatudor]

Sorry, I should have been clearer, was just finishing a 12 nightshift when I wrote it. The wire to the battery via the ignition switch goes to one side of the alternator indicator light, this will always be at the battery voltage when the car is running. The other wire going to the alternator indicator light goes to the alternators IND terminal. So you got it right, no thick skull.

There is no hard connection to ground, the voltage on both wires will be the same when the alternator is charging correctly at 12V. Because there is no voltage difference between the two wires the light will be off. When the alternator stops charging or producing enough current to charge the battery then there will be a difference between the two wires and the light will start to illuminate. It will be the brightest when the alternator is making no charge ie the engine is off (or sometimes idling too slowly) or the alternator drive belt is off. It may illuminate slightly when you have all of your accessories on with high beam etc and the alternator is struggling to output enough charge to match the load.

So your reasoning is on track, with both voltages pushing against each other if both are equal then there will be no light when one is lower then current will flow and the light will come on.
I hope this clears up my first post.

[seasanford]

I thank you very much sir, the fog has lifted.