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Discussion Starter #1
I have a 68 that I rewired with a painless harness. As shown in the painless book I hook wire #914 (should be white according to docs, but really is brown) to the alternator regulator exciter. I then hook an 8ga wire from the output lug to a junction block that goes directly to the battery. The alternator is a CS130 with the 4 prong connector for the exciter wire & voltage sensing wire. As shown in the techref doc I hooked the "L" prong to the exciter wire which has 12v when the key is in run, and the "S" terminal with the thicker wire straight to the alternator output lug. "F" & "P" are not hooked to anything.
My first alternator was a rebuilt unit and did not work when I started up the car. I had it tested and it was bad so I picked up a new one and had it tested before leaving the store. When I installed it in the car and started it up I got only 12v and it appears this alternator is bad now as well. I'm somehow burning them up! Any guesses at all as to what this would be and I would greatly appreciate it. I've spent 2 years getting the car to this point, and I can't run the car!!
- I'm not running an "idiot" light. Could this cause a problem since there is no resistor between the internal regulator and the batt power?
-What is the "F" terminal on the alternator for? It has a wire, but is not hooked to anything per the tech ref doc.

[ 03-31-2004, 06:00 PM: Message edited by: ramcda ]
 

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The L wire is for the idiot light. I'm not convinced that the L wire needs a 12 volt source and often hear to it referred to as the exciter. Disconnect it and see what happens. But you do need resistance in that line as it applies a direct short to ground when the light is on (during a failure). That would explain the burning sensation you are getting.

If you disconnect the L wire and it doesn't work (presume no smoke has gotten out) install a resistor between 12 volts and the L wire. The resistance should approximate the bulb filiment. I'd try 680 ohms at 1/2 watt.
 

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Discussion Starter #3
I'm a bit confused. A trip to auto zone indicated that I indeed damaged the alternator as it tested fine yesterday. I took the opportunity to take a look at their adapter they use for testing and the power to the "L" terminal was fed through a light yielding 20 ohms of resistance with the multimeter. This leads me to a few very specific questions. I have a new alternator now and I'm scared to death to install it at this point.

- The "L" terminal is for the idiot light as Dnult mentions. It is also the "exciter" terminal. Does the term "exciter" indicate that power on this wire is what "turns on" the alternator? With the key in run and engine off the idiot light should be on as the "L" pin is a ground. Does this mean once the alternator is spinning the "L" pin is no longer a ground?
- Is a wire to the "L" pin even needed if I'm not running an idiot light?
- The adapter they use at auto zone has a wire fed into the "F" terminal. The tech ref doc indicates this pin is not used. What exactly is the "F" pin for?
- Would not having the resistor on the wire immediately burn out the internal regulator on the alternator when the key was turned to "run" since the "L" pin is a ground at that point?
 

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Here you go:

http://www.novaresource.org/alternator.htm

"Most of the connectors for the CS alternators are four wire but you will only use two of them and the wiring is the same as the SI.

S = a heavy gauge wire to the battery supply (horn relay)
F = not used
L = a small gauge wire that comes from the idiot light and energizes the alternator
P = not used

You need to purchase or make a conversion adapter that is just 2 short wires and 2 connectors. One is a CS connector to plug into the alternator, the other is a female connector to accept the SI plug from your original harness. There are two different types of conversion adapters. One is a non-resistor and the other has some resistance built-in it. The "L" wire that energizes the alternator needs some resistance (35 ohms or more) in it otherwise it will cause the alternator to fail. If you have a warning light in the dash and use the stock wiring to it then that bulb serves as the needed resistance and you should use the non-resistor adapter. If you don't have that bulb or have less than 35 ohms resistance in the "L" wire then you will need the adapter with resistance built in. If the "L" wire has more than 350 ohms then there is a problem with that wire and it will need to be fixed.


Non-resistor adapters:
- AC Delco: 8077
- Haywire: 2110
- Painless Wiring: 30707

Resistor adapters:
- AC Delco: 8078

Or:

http://www.camaros.net/techref/ftecref14.html
 

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The bulb resistance may be 20 ohms cold, but lit it will increase significantly. But bulbs disipate their power as heat and light. Resistors on the other hand disipate power only as heat. So if you put a 20 ohm resistor in circuit, you'd be disipating 14^2 / 20 watts or 9.8 watts. That's a dang hot resistor. The bulb is probably more like a 1 watt bulb or less. So that means the bulb filement is more like 392 ohms. So the answer to your question is no, the resistor won't burn up, so long as you don't make it too small in value and too low in wattage. But you have to be practical. You could install a 2 watt resistor in there but the thing would get so hot you'd have to worry about it melting things.

You won't burn anything up by disconnecting the L line for a test. If it is in fact an exciter then the alternator won't put out and it will be evident by the battery voltage measurement. But I believe the light output is really a fault circuit created by an open collector transistor that the regulator turns on during a fault condition. And no, the resistor I recommended will not burn up the resistor or the regulator.

I am not sure what the other two terminals are for, including the F terminal. I haven't found any technical documentation specifying what it is, but I know it works without it just fine.
 

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Discussion Starter #6
As always this site amazes me. In a few short hours I have the answer to a problem that would have taken me a month to solve. How did people live without the internet?

Dave & Mark - Thank you!!!
 

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Let us know what you ended up doing. It's one thing to give advice and another to know it worked.
 

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WOOHOO!!! It works.
After a whole lot of research on this and many other websites I was unable to find an exact figure of exactly what resistor came in the harness that GM sells for this purpose. I went ahead and purchased AC Delco P/N 8078 and dissected it to get the exact value of the resistor before wiring it into the car so that others will not need to pay $25 for a 25 cent resistor. The colors on the resistor were Red-Brn-Brn-Green. I thought the color code was only supposed to be 3 digits + Gold/Silver indicating the tolerance??? When measured with the multimeter set to 2K ohms it measured .506 . Does this indicate a 1K Ohm resistor? That seems excessively high, but it works fine.
 

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Backwards. . . reverse the color code (Red-Brn-Brn-Green) to Grn-Brn-Brn-red and we have a 511 ohm 2% tolerance resistor. Many a-time I've had to pick up the DVM to double check resistors. The gap between the last and second to last band isn't always easy to tell.

Bob.
 
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