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Old 09-12-2018, 11:24 AM   #1
fredhlynch2
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The Mysterious "L" wire CS 130 Alternator

I have a GM serpentine system for my small block in a 64 C10. I switched over to a later alternator and got rid of the external voltage regulator. Now I need to wire the new CS 130 that comes with the serpentine kit. It says to run the "L" wire to the idiot light. No idiot light, just gauges. So how do excite the alternator if I have nothing to attach the "L" wire to? I have looked everywhere on the internet and they suggest attaching a resistor and/or run the wire to a light. Is it that simple? How would you wire this light in series?

I hate all things electrical and just need a diagram showing how to do this.

If I run the "L" wire to a light do I just ground the light? Does the "L" wire provide positive electrical feed? Will the light always stay on if the alternator is charging? I could live with a light in the dash if it goes out once the alternator is charging.
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Old 09-12-2018, 08:22 PM   #2
ray_mcavoy
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Re: The Mysterious "L" wire CS 130 Alternator

First, check the terminals on your alternator to see if they are marked "P L I S" or "P L F S".

If yours is marked "P L I S", you can use the "I" instead of the "L" terminal. The "I" terminal is simply connected to a source that's switched on/off via the ignition. No need for a light or resistor.

But if your alternator is marked "P L F S" you'll need to connect the "L" terminal to a resistor (35Ω minimum) or a light. The other side of the resistor or light should be connected to a battery voltage source that is switched on/off via the ignition. If using a light, it will function just like the "gen" or "alt" light in a truck without gauges.
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Old 09-12-2018, 08:31 PM   #3
dmjlambert
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Re: The Mysterious "L" wire CS 130 Alternator

More info in addition to ray_mcavoy's great info. I was just about done typing this when he posted, so I thought I would go ahead and add mine:

Discussion here in this post, about 12SI and CS130 alternators and the wiring for them. Post #17 by VetteVet has the diagrams and pictures and lots of great info. He's suggesting an 85 ohm 5 watt resistor.
http://67-72chevytrucks.com/vboard/s...35#post8254935

Here is a guide from AAW:
https://www.americanautowire.com/PDF...20IN%203.0.pdf
They mention you can use anything between 35 ohms (5-Watt resistor) and 500 ohms (0.5 Watt resistor). The larger number of ohms the less current it will draw so that means smaller watt rating would be fine for larger number of ohms. I wrote an email to AAW to ask them what size resistor they put in the AAW ready-made adapter they sell, and Marc DeMontigney wrote back and said 510 ohms. Forum member driller35 wrote in post #80 of the "Alternator question" thread I mentioned above that the ACDelco adapter has 511 ohms in the wire, so I'm thinking that is a 510 ohm resistor plus small amount of wire and connector resistance. Resistors have a certain amount of guaranteed tolerance, and that is what percentage different number of ohms that they actually are compared to what they are marked or sold as. So 500 ohm resistor is not going to be exactly 500 ohms, but it will be close enough for Chevy work.
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