Charge indicator light - huh? - Pontiac GTO Forum
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post #1 of 17 (permalink) Old 12-03-2012, 11:36 AM Thread Starter
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Charge indicator light - huh?

Put your feet up and settle in, this one has me a little baffled.

I need some help getting my charge indicator light (the "GEN" light) on my 69 GTO to act right.

Here's some background: The car originally had a Delco Remy 10DN alternator with external voltage regulator, as most did. However, that system didn's supply enough current to keep up with my system after adding those big honking twin electric cooling fans (30 amps each) so I converted to an internally regulated CS130 alternator that puts out 105 amps. Here's how I connected/converted it:
The CS130 has a main BATT connector for the output, plus a 4 pin connector that has terminals labelled S I/F L and P. "S" is for "sense" and it needs to "see" the alternator's output so the internal regulator has a reference to control alternator output. I/F is a connection to Field positive and normally isn't used. L is the connection for the charging indicator light. P is connected to the stator and is normally used as an input to a tachometer or engine hour meter (like on an airplane) - also not usually used in a car.
So, in the Beast I have the CS130 connected like this:
Batt goes to the main alternator output (fat wire that goes to the starter solenoid terminal - same as with the stock alternator). I put a short jumper from the Batt terminal to the S (sense) terminal on the alternator. The L terminal is connected to the black wire with white tracer in the original engine harness that goes back to the original external voltage regulator connector (one of the "middle" two terminals on the VR connector). At that connector, the brown wire on one end of the connector goes to the indicator light in the dash - eventually. When I converted to the CS130, I left the extrnal VR installed but just unplugged the connector and used a jumper wire to connect the brown wire to the black/white tracer wire which completed the circuit from the light to the L terminal on the alternator.

Everything was working fine. The light worked like it was supposed to ("on" with key on, engine off - "off" with engine running). Until a few days ago.

I was driving the car and the light came on. I checked the alternator output with a meter when I got home, and sure enough it was only making about 13.5 volts instead of the needed 14.4, so I replaced the alternator (under warranty) and verified the new one is making 14.4 volts output just like it's supposed to.

However, now the light isn't cooperating and I haven't been able to figure out why. It doesn't make sense.
Here are the symptoms I've identified so far.
* Engine running - light is on, brightly - this isn't right.
* Ignition on, engine off - light doesn't come on - or maybe it's on but very very faint. Sometimes it wil flash briefly, but doesn't stay lit. It acts the same way if I turn the switch to ACC - I don't think this is right.
* Completely remove the jumper at the VR connector - then if I turn the ignition on, or turn the switch to ACC, the light comes on and stays on - brightly - I don't think this is right.
* Ignition off, engine off, jumper disconnected - if I apply 12v to the brown wire at the VR connector, the light is on bright - I think this might be right?

My understanding of how the light circuit is -supposed- to work, is that with the ignition on, engine off, the path through the light to the L terminal ultimately goes to ground, completing the circuit, and turning on the light. When then alternator is charging however - alternator output voltage is feeding 'back' out the L terminal instead of going to ground so there's no current flow to turn the light on. I'm not 100% positive if that's how it really works or not. (Does it?)

With all that in mind, I'm at a loss to explain why it's doing what it's doing.
If there was an 'open' in the light circuit, why does it light when I remove the jumper or apply 12v to the brown wire at the VR connector?
Why does the light come on with the jumper removed (well, obviously it has a path to ground somehere 'after' the light but 'before' the connector - but then if that's the case why don't I have a dead short when I apply 12v to the connector?)

This is driving me nuts.

Bear

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post #2 of 17 (permalink) Old 12-03-2012, 12:29 PM
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Sir, I wish I had some insight but I pretty much don't. I have to SEE the circuit and get my hands on it to even come close to troubleshooting it. That said, what changed? It was working for a few months, the alternator went poof, and now, the light is staying on. Something changed in the light circuit, and it may or may notbe related to the old alternator going South (no offense!). You had it working before, and it's not working now. The only thing you changed out was the alternator. If the circuit is fine, possibly a defective new alternator??
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post #3 of 17 (permalink) Old 12-03-2012, 01:23 PM
 
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Bear,
This may help:

Delco Remy CS130 & CS121 Alternator Repair Manual - Page 1, Introduction to the Delco type CS130 and CS121 Series alternators

Larry

2005 GTO Fast - 2004 Z06 Faster - 1984 Honda V65 Magna Fastest
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post #4 of 17 (permalink) Old 12-03-2012, 02:57 PM
 
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At first glance, my guess is that the "L" terminal is not being "ungrounded" when the voltage comes up. Not sure why, maybe a fault in the "L" terminal itself, the wire in the harness at some point has now vibrated enough to rub the insulation off and is grounding itself. I would probably try disconnecting the "L" wire, ohm it towards the harness, would guess it would be open with the ignition switch off. With the ignition switch on, you should measure ~12V. Troubleshooting guide suggests using a fused test wire to ground the "L" wire should turn light on/off. Not sure how the VR jumper is wired, does it jump certain pins together or?? Verify the VR jumper anyways to make sure it is doing what it is supposed to do.

Last edited by the65gto; 12-03-2012 at 03:22 PM.
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post #5 of 17 (permalink) Old 12-03-2012, 07:04 PM Thread Starter
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It's still not making sense - so I'm gearing up for some serious exploration. I just have to get my mind right about digging into it because getting access under the dash is probably going to mean pulling out the driver's seat and dropping the column, which is a mild pain due to the ram air cable bracket, but I guess there's no avoiding it. I've still got the original wiring harnesses that I replaced with M&H, so maybe I can use that to figure out how things "should" be.

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post #6 of 17 (permalink) Old 12-03-2012, 09:25 PM Thread Starter
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Well, ok - I spent some time with a meter and with the old wiring harness, and I think I'm onto something. If I'm right, the problem might actually be in the new alternator.

Using the wiring diagrams, my meter, and my old harness, here's what I've learned so far.
Power comes off one of the ignition switch "on" terminals and goes to the firewall connector at the back of the fuse block. From there, it splits and goes two directions: one direction goes to the indicator light and then through the light to ground. This means that even with the alternator wire disconnected, it's normal for the indicator light to be on when the switch is on. So far so good. At the point on the firewall connector where it splits, the other side goes through the brown wire to the voltage regulator connector (and originally through the voltage regulator) and out from there through the black wire with white tracer to the alternator (the "L" terminal in my case).

I haven't yet found enough detail that tells me exactly what's supposed to happen at the L terminal inside the alternator, so from here on I'm just making an educated guess based on how it's acting and what I know about the rest of the wiring. Given the light circuit wiring on the 'other end' of the harness, the only way that the alternator side of the circuit could work in order to turn the light on and off would be for the L terminal to provide no (or a very high resistance) path to ground with the alternator not charging, and to provide a very low resistance path to ground when it is charging. When resistance is high, current to the light circuit will flow through the light and turn it on. When resistance is low (significantly lower than the light bulb) then current will take the "easier path" and flow through the alternator to ground instead of to the light. This sort of behavior is sometimes accomplished through creative use of diodes, and I know alternators have diodes in them, so I'm wondering if maybe this alternator has one or more "backwards" diodes in it - because that's how it's acting - the light is working "opposite" of how it should be.

That's the only thing I've figured out that makes sense based on how it's acting.

Thoughts?

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post #7 of 17 (permalink) Old 12-04-2012, 08:29 AM Thread Starter
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Well, pooh.... after that carefully reasoned out explanation of how the circuit works, I remembered I still had my old (non-Rallye gauge) cluster around so I got that out to continue following the circuit through the light bulb and on to the other side. Turns out that my carefully reasoned explanation was -- completely wrong.

I've got more research to do...

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post #8 of 17 (permalink) Old 12-04-2012, 03:44 PM
 
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Bear,
I've looked at a few 68-69 wiring diagrams and the brown wire that went to the #4 position on the original
regulator is the idiot light wire. It should be connected to the "L" terminal of the new alt. This is all the
control wires needed to make it work. The circuit from the Ign switch "I" terminal, to the idiot light, then out to
the old regulator, is all that is needed. On new cars there is a resistor across the idiot bulb, so if the bulb
blows, there will still be a circuit to the "L" terminal of the alt.

Larry

2005 GTO Fast - 2004 Z06 Faster - 1984 Honda V65 Magna Fastest
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post #9 of 17 (permalink) Old 12-04-2012, 04:22 PM
 
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Hey Bear, I have a 10 si, hooked similar to yours, Should be 12v + with key on to one side of the indicator lamp , and straight to the alternator from the other side of the lamp......... and as you had mentioned the voltage cancels out when the alternator is charging check out the pirated thumbnail.
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post #10 of 17 (permalink) Old 12-04-2012, 04:33 PM
 
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I am wondering how the VR bypass jumper is wired or connected, eventually I will be installing another alternator on mine with the internal regulator. Bear, do you have faith in the place where you bought the alternator to be able to test it at their location for all functions, light on/off.?
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