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Old 01-06-2018, 11:20 PM   #1
SunSoaked
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Alternator Wires?

In the process of swapping a serpentine drive system from a 95 into my 85. They both have 3 wires but the heavy red wire on the 85 was cut coming out of the plug and I can't find the other end of it. The new one has a pink/black wire (smaller gauge). Does this pink/black wire go to always hot or ignition?
Thanks
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Old 01-07-2018, 03:10 PM   #2
VetteVet
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Re: Alternator Wires?

Quote:
In the process of swapping a serpentine drive system from a 95 into my 85. They both have 3 wires but the heavy red wire on the 85 was cut coming out of the plug and I can't find the other end of it. The new one has a pink/black wire (smaller gauge). Does this pink/black wire go to always hot or ignition?
Thanks
There are a few variations of the wiring as the more modern vehicle alternators were developed. Two things that has stayed the same are, The large red output wire is connected to a junction with the battery positive and all of the current loads in the vehicle.
The other is that the smaller exciter wire is brown, and it connects to a "key on" power source, with a resistance inline, to protect the diodes in the alternator.

In the earlier years there was a third wire, also smaller, that was a voltage sensing wire, the purpose of which was to tell the internal regulator to increase or decrease the output of the alternator fields as needed to maintain the 14.5 volts output.

These alternators after the CS was introduced had a four wire plug in the alternator body labeled FSLP or PLIS . the L terminal was the ignition connected exciter wire, and the S was the voltage sensing wire. The P was rarely used and the I was used as a charge indicator to a light in the dash.

This picture illustrates the terminals and the ones used to convert the CS style to the older trucks and only the L and S terminals are used, even though there are wires to the terminals F and I.

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This is the 85 diagram, bottom is the alternator hookup. notice the large red and the smaller brown and red wires.

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This is the 85 cab connections, notice the brown wire from alternator on the dash connections on the upper right. This is the exciter wire.

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This is the 88 to 98 diagram. The alternator wires are still red and brown, but there might be a wire in the plugin to the ECM or the PCM that is a charge indicator and it might be the pink/black wire you have. It is my understanding that in 1995 there was only 1 brown wire from the alternator plugin and the voltage sensing was done by the ECM. Also the alternators did not need any external resistance to protect them. Wiring in a resistor in series with the brown wire should not hurt anything in case the 85 does not have this protection or your alternator may not have internal protection.

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This is the in cab diagram and it shows the brown wire from the alternator just like the 85.


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88 to 98 is a broad spectrum so it may be that the pink/black wire is used in the later years but not as the ignition supply wire. Further research is needed before I could say whether it is constant hot or ignition hot but as far as I know only the sensor wire is constant hot and I believe the P/B wire is an indicator wire. That means you have to locate a brown ignition exciter wire in the 85 harness. I hope this helps.
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Old 01-07-2018, 05:17 PM   #3
VetteVet
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Re: Alternator Wires?

Here's a link with a lot of info.

https://alternatorparts.com/cs130-sbpage1.html
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Old 01-07-2018, 10:52 PM   #4
SunSoaked
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Re: Alternator Wires?

Thank you Sir for the reply! This is great info. I think I can figure it out now.
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