CS130 Alternator and 2 wire Idiot Light wiring help

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Tynan918

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Aug 2, 2021
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CS130 Alternator, 3 wire plug and 2 wire Idiot Light install...

How can I wire this 2 wire idiot light to my CS130 alternator ? I've been trying to decode this wiring setup/route for 4 hot days now...

Idiot light has two wires running from it, brown and black.

Alternator has a 3 wire plug, and on it the wires are labeled "SFLP" (P has no wire.).
IMG_20220615_173712902_HDR.jpg



Screenshot_20220615-175835-197.png



I'm told: "S" wire goes to the alternator battery stud, F isn't used if I'm using the idiot light, "L" is wired to the idiot light power wire (brown), and there is no wire for "P" on the plug."

I have the "L" wire attached to some wire I extended through the firewall and attached to the brown wire at the idiot light and a ground wire running straight from the negative battery terminal, but the light doesn't power on when I turn the key on...

Only way I get the idiot light to power on once the key is in the on position, is if I have the "L" wire also connected to the battery stud on the alternator, but when the key is turned off, the idiot light won't turn off until I disconnect the wire...
 

Tynan918

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Aug 2, 2021
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Screenshot_20220618-191100-103.png
Screenshot_20220618-191032-138.png
 
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79 USA 1

Royal Smart Person
Sep 2, 2011
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Hoping I can explain this, Please understand I'm not talking down ...it just took me some studying the GM wire diagram to make sense of this change over.
Here goes...
The idiot light bulb is used as resistance to "excite" the regulator into charging. One side of the bulb runs to the #39 Circuit which has 12 volts on it when the ignition is switched on. The other side of the bulb runs to the #25 circuit which in the original set up would be your brown wire going to the alternator. When the alternator is not charging (Spinning) the #25 circuit becomes a ground thus lighting the light.
Now with your new set up The "L" terminal should be wired to one side of the light socket (Becomes circuit #25) and the second side of the light socket lead should go to your fuse box under the dash into a port marked "IGN". That is a 12 volt hot with key on source (Circuit #39). The light should illuminate with the key on engine not running, once started, alternator turning, The "L" terminal should now produce 12 volts and no longer light the idiot light. You should then have 13.5-14.2 volts (Charging) going into the battery.

Hope this helps.
 
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TType85

Not-quite-so-new-guy
Apr 26, 2017
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Garden Grove, CA
I recently had an issue when I put my new wiring harness in the car (1986 Buick Regal T-Type). No stock wiring in place (Holley Dash) so no idiot light. Close to new AC Delco Gold alternator.

It is exactly like what 79 USA 1 said.

It should have worked with keyed voltage to the F terminal but it didn't; no charging.

I ended up putting a bulb on the L wire and it worked (Keyed voltage --> bulb --> L terminal). Key on engine off the bulb should light; start the car and the bulb should go out and the alternator should be working. The voltage the alternator puts out basically cancels the ground path for the light; the "ground" is the alternator when it's not running.
 
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Tynan918

Royal Smart Person
Aug 2, 2021
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Hoping I can explain this, Please understand I'm not talking down ...it just took me some studying the GM wire diagram to make sense of this change over.
Here goes...
The idiot light bulb is used as resistance to "excite" the regulator into charging. One side of the bulb runs to the #39 Circuit which has 12 volts on it when the ignition is switched on. The other side of the bulb runs to the #25 circuit which in the original set up would be your brown wire going to the alternator. When the alternator is not charging (Spinning) the #25 circuit becomes a ground thus lighting the light.
Now with your new set up The "L" terminal should be wired to one side of the light socket (Becomes circuit #25) and the second side of the light socket lead should go to your fuse box under the dash into a port marked "IGN". That is a 12 volt hot with key on source (Circuit #39). The light should illuminate with the key on engine not running, once started, alternator turning, The "L" terminal should now produce 12 volts and no longer light the idiot light. You should then have 13.5-14.2 volts (Charging) going into the battery.

Hope this helps.
I watched this video here on 10SI to CS130 conversion 3 wire plug idiot light/resistor wiring :

Seems straight forward, quick, and simple, so this is what I want to do with it, but I have a few questions before I buy this harness at my local NAPA (Advanced, Oreilly's, nor Autozone carry the harness)... ACDelco Professional PT2145 online or NAPA Echlin Ignition part # ECH EC82.
Screenshot_20220619-201653-623.png


Is this route eliminating the idiot light ?

The guy in video shared said to cut the connector end of the harness and wire the "S" wire (red wire) to the battery stud on the alternator. The "L" wire (yellow wire) has a resistor fused with the wire and resistance is rated at 511 ohm, and runs directly to a clean switched ignition connection.

With the idiot light acting as a resistor and the "L" wire having a resistor fused in it, does this eliminate the idiot light altogether ?

Secondly, the "clean switched ignition source"...
Screenshot_20220615-021508-987.png

Screenshot_20220619-210453-635.png


My best guess would be these IGN connector on the fuse block (labeled green in first picture, circled and marked with red in the second picture). I've tested these and there is 12v when the key is turned on only, off there is no voltage at these connections.

What wire connector do I use to plug the "L" wire from the alternator plug harness into this size connector ?
 

79 USA 1

Royal Smart Person
Sep 2, 2011
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Cheektowaga, New York
Judging from the video you can eliminate the incandescent warning light with the harness that has the resistor. That being said he also mentioned he still uses the light bulb as a visual aid which is really only lit with the key on engine not running. That would be your choice.
As far as the fuse block...Yes that is where you want the "L" wire to run into. It is technically the #39 Circuit I had mentioned before. In my 79 Monte Carlo I added an electric choke feed wire that uses one of the top positions you have marked in red. I used a standard male crimp on blade connector to fit into the fuse panel.
Hope this helps you out.
Bob S.
 
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Tynan918

Royal Smart Person
Aug 2, 2021
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Judging from the video you can eliminate the incandescent warning light with the harness that has the resistor. That being said he also mentioned he still uses the light bulb as a visual aid which is really only lit with the key on engine not running. That would be your choice.
As far as the fuse block...Yes that is where you want the "L" wire to run into. It is technically the #39 Circuit I had mentioned before. In my 79 Monte Carlo I added an electric choke feed wire that uses one of the top positions you have marked in red. I used a standard male crimp on blade connector to fit into the fuse panel.
Hope this helps you out.
Bob S.
Yes sir, that helped me, thank you 👍🏾
 

Tynan918

Royal Smart Person
Aug 2, 2021
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79 USA 1 Guys in that Monte Carlo Facebook group keep telling me I need a 4 gauge wire running from the battery to the alternator...since I have a higher than factory amp alternator.

Is this true ? My alternator is rated at 105 amps

Screenshot_20220621-064658-901.png


If so, I know I need a 3/8 ring connector on one hand of this wire, but what is the size of the other end for the alternator stud, 5/16 ?

Screenshot_20220621-064950-808.png
 

64nailhead

Goat Herder
Dec 1, 2014
5,659
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Upstate NY
4 gauge is needed (or is the best option.)

I choose to run the 'idiot' light. It's a quick way to know that there is an issue rather than not noticing the voltmeter is reading in the 'bad' range. My son has melted down several alternators due to a low budget header we bought and repaired about 5 times. The 1st sign of a cracked manifold was the alternator light would illuminate. Me and the local alternator rebuilder were on a 1st name basis back then haha
 
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