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Old 09-19-2009, 01:01 PM   #1
MrBill
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Default How to make an alternator exciter/warning light?

Okay so the car in question is a 78 244. It shouldn't matter what it is though.

On my 242, I simply hooked up a switched 12v source to the alt and ran it that way. It gave me two problems.
  • the car would run on for a second or two
  • I had no indicator if the alternator was working

I plan on putting this cluster I made and that means the old one goes away. I want to take a blank plate on the center console and drill it for four lights.
  • left/right turn signal
  • oil pressure warning light
  • alt exciter.

The important/difficult one is the alt exciter. How exactly does this guy work? When the alt is not charging, electricity is traveling to the light (which I'd like to be an LED) but somehow (via a magic diode or something) the alt charges and the light goes away.

Please, gods of cars, assist me.
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Old 09-19-2009, 01:11 PM   #2
nathaninwa
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i wonder the same thing....these units look and run just like the oldschool gm ones. Simple fix, or test with a light tester. leave the charge wire as is, on the single switched wire, simply install a 1156 (led will need more resistance). The alternator not working...charging is acting as ground, one the reg is exited via the wire, it to puts out 12volts + and turns the light off.

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Old 09-19-2009, 01:22 PM   #3
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1156 is wayyy to big. Needs to be tiny
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Old 09-19-2009, 01:35 PM   #4
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On the original setup of a alternator light, the light is in series with the switched power to the exciter.
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Old 09-19-2009, 02:55 PM   #5
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then try a peanut bulb like the older american cars run for marker lights and dash lights.
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Old 09-19-2009, 03:00 PM   #6
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okay so I think I'll try this out, sounds simple enough.

I just take a switched 12v source, go through a 12v light, and go to the alternator.
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Old 09-19-2009, 03:04 PM   #7
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you got....just like the other post....in series with the exciter wire
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Old 09-19-2009, 05:23 PM   #8
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it seems so magically simple.

off to more threads about the car.
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Old 09-19-2009, 07:56 PM   #9
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In the typical hookup it is not that simple.

The alt. control wire is used for two purposes:

1) One to alert the driver of a failure in the electrical system, alt., belt or maybe wiring in the charging circuit.

2) When the alternator is not turning as when the engine is off but ignition on it functions to light the dash warning lights as a light test mode.


It requires a bulb in a certain current range so if replaced with an LED type polarity is important and it may have to have a resistor added to maintain the proper current. The current range is also designed to function over varying temperatures and types of regulators. I would check the typical current draw of the alt. light used and keep it the same with your replacement.
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Old 09-19-2009, 08:07 PM   #10
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What Nathan said:

The alternator idiot light operates like this: 12V from the 'run' circuit (don't know the fuse #) that travels to the idiot light and then to the alternator. In the circuit, the alternator is either a ground (engine not running) or as a voltage source. When the engine is not running the alternator completes the circuit and the idiot light is on. After the engine starts, the voltage from the idiot light floats when the alternator starts charging. Since there's no difference in voltage potential, the lamp stays off.
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Old 09-19-2009, 09:09 PM   #11
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Right I realize I can't use an LED for this. I'll look into the current draw of the alt light and try to match it up. It needs to be small though. On those blank panels i need... two for turn signals, high beam, oil pressure warning, innovate wideband light, and this alt light. I can't fill them all up or it will look stupid
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