Alternator "buzzing" or "humming" when car is off, battery dies

Wondering if anybody has experienced this one.

Background: 1996 LT1, factory harness reworked by Speartech. I finally got my LT1 running and took the car for a spin around the block. Frickin' sweet!! :smoke:

Instead of disconnecting the battery cables like I usually did durning the project build, I figured I'd leave everything connected. (this is how I will usually "store" the car for a week or two at a time) The following Saturday I put the keys in... nothing... dead battery. :machine:

Well, long story short, my faithful Optima red-top gave up the ghost after 6 hard years. So I bought a new one, installed it, everything worked great... until I came out to the garage the next morning. I heard a faint buzzing or humming... lifted the hood, and the sound is coming straight from the alternator. Sounds like the voltage regulator is buzzing. So I disconnected the plug that goes to the alternator... buzzing stops. Take my multimeter after it... sure enough, I'm getting voltage feeding from one of the wires to the alternator.

Is the alternator supposed to get voltage when the car is off? Is this a case of Speartech wiring it up to a constant hot versus a switched hot by accident? Yeah yeah, I'm going to call them, but I wanted to get educated before I go pointing fingers on who is to blame.

Oh, and the alt. checks out OK according to the factory troubleshooting guide.

exactly. the alternator is only supposed to get voltage with ignition on. its draining your battery :)

I figured as much. Great. Now I need to figure out how to fix this... one disadvantage to mail order wiring harnesses. :hammer:

Interesting... just called Speartech. He's saying it does indeed get power when the igntion is off... I'm going to get some more information to John to see if he can help me troubleshoot this.

I thought alternators had 3 wires, a battery charge lead (BAT stud) that is always hot, a load sensing wire (the red one in the connector) that is always hot, and a trigger lead (the brown wire that goes to the idiot light or resistor) that is hot in RUN/IGN. If that brown wire is hot when the car is off the alternator will be 'on' and cause a drain.

Do I understand this correctly?

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Originally Posted by BonzoHansen

I thought alternators had 3 wires, a battery charge lead (BAT stud) that is always hot, a load sensing wire (the red one in the connector) that is always hot, and a trigger lead (the brown wire that goes to the idiot light or resistor) that is hot in RUN/IGN. If that brown wire is hot when the car is off the alternator will be 'on' and cause a drain.

Do I understand this correctly?

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Sounds correct for an old school internally regulated alternator. Perhaps this changed over the years? :confused: I'm sure the wire colors have changed.

I belive my 140 amp alternator has a 3 pin connector that goes to the alternator in addition to the BAT stud. I've been instructed by Speartech to find out what the pins are labeled as on that connector, and which one the voltage is coming out of.

im using a stock alternator from an 89 iroc which is a 4 pin plug I believe but I only have the main battery cable running to the stud of coarse and one ignition wire running to the 4wire plug. and it works fine, no load sensing wire and no 'low voltage' to dashboard wire.

It is funny you mention this. I HAVE THE EXACT SAME FREAKING PROBLEM. I have been trying to track it down for weeks. And here is the strange thing, it is a 95 LT1 & the harness is reworked by John at Speartech. But I can't blame John, the wire that is feeding the alternator power to charge is the factory Monte harness. It's the brown wire from under the dash somewhere on the driver's side, key on I get 12v, key off I get .43 volts.

My 95 alt only has 2 wires going to it, one is the big one that charges the battery, the stud on the back of the alt & the other is a single wire in the plug that energizes the magnetic field.

maybe a bad ignition switch or relay depending how its wired that is allowing voltage to leak by still?

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Originally Posted by TraviZ28

maybe a bad ignition switch or relay depending how its wired that is allowing voltage to leak by still?

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I unplugged my steering column & had the same results. So that ruled out the switch.

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Originally Posted by 69LT1Nova

Sounds correct for an old school internally regulated alternator. Perhaps this changed over the years? :confused: I'm sure the wire colors have changed.

I belive my 140 amp alternator has a 3 pin connector that goes to the alternator in addition to the BAT stud. I've been instructed by Speartech to find out what the pins are labeled as on that connector, and which one the voltage is coming out of.

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They have not really changed. I use a CS130 and use 3 wires in my 77. I know I wired the the OE brown wire (idiot light) to the alt L terminal. For retrofits if there is no idiot light people put a resistor inline in place of the light.

What I don't know is the swap specific details, like if the alt goes through a BCM or something stock. I found this diagram for 96 Camaro on the auto zone site. Vin P is the V8. Does not look like it does for the V8 car, but I also see no S wire.
https://static1.pt-content.com/image...800b882e-1.gif

For the record, on my car:
Bat (red) hot constant
S (red) hot constant
L (brown) hot IGN

Just seeing if any of this helps any one and that my understanding is correct.

If we were to put a resistor in the brown wire (only wire on the alt other than the charging wire to the battery), then the resistor may drop the voltage to the alternator, but would still draw current from the battery & potentially drain it.

Here is a 95 F body LT1 charging/starting circuit diagram:

http://shbox.com/1/starter_charging_95.jpg

same diagram for 1996 F body
http://shbox.com/1/starter_charging_96.jpg

maybe you should trace the wire back and re route it directly to your starter solenoid? that is how mine is run, and it won't get voltage till my ignition trips the solenoid.

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Originally Posted by TraviZ28

maybe you should trace the wire back and re route it directly to your starter solenoid? that is how mine is run, and it won't get voltage till my ignition trips the solenoid.

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Then when the solenoid is disengaged (key in run position, not start), won't the power to the alt go to 0? Also if I was to do this, i am betting my gauge won't work.

You are right, I must have not been thinking clearly when I typed that up. You could put a new relay in line, but that would really just be a band aid for the problem. I am just suprised that wire is drawing voltage with all keys off.. I tested mine today and I have zero voltage with key off and my wire does in fact run back into the factory ignition switch. I have been no help here .

Quote:

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Originally Posted by TraviZ28

You are right, I must have not been thinking clearly when I typed that up. You could put a new relay in line, but that would really just be a band aid for the problem. I am just suprised that wire is drawing voltage with all keys off.. I tested mine today and I have zero voltage with key off and my wire does in fact run back into the factory ignition switch. I have been no help here .

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LOL. Seems to be my luck, no one has any suggestions that I haven't already tried. Seems to be a mystery that no one can solve. Maybe 69LT1Nova will have some info on it.

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Originally Posted by Samckitt

Here is a 95 F body LT1 charging/starting circuit diagram:

http://shbox.com/1/starter_charging_95.jpg

same diagram for 1996 F body
http://shbox.com/1/starter_charging_96.jpg

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Better diagrams because they show more IP detail. So it looks here like the 2 red on other GM alts is replaced by just the one red with voltage sensing now in the alt, and the brown wire still goes to the IP (no pcm or bcm). Do I see a 470ohm resister in the L circuit? Or am I reading this wrong? I still think that brown wire should be hot IGN only.

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Originally Posted by BonzoHansen

Better diagrams because they show more IP detail. So it looks here like the 2 red on other GM alts is replaced by just the one red with voltage sensing now in the alt, and the brown wire still goes to the IP (no pcm or bcm). Do I see a 470ohm resister in the L circuit? Or am I reading this wrong? I still think that brown wire should be hot IGN only.

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I agree, brown wire SHOULD be hot in run only. Forget the LT1 harness, on mine the ALT is energized from the factory wiring in the 86 Monte. So my problem lies in it somewhere. With my key in the run position I have 12v at the end of the brown wire (disconnected from the ALT), and .43v with the key off. I haven't pulled the gauges out yet to see if something is wrong with them.

What a PITA... here are some pics of what is going on.

The connector:

https://static1.pt-content.com/image...PICT0904-1.jpg

Voltage through the "F" terminal wit the ignition off:

https://static1.pt-content.com/image...ICT09061-1.jpg

I just got off the phone with John at Speartech. He let me know that the F terminal is to the field of the alternator. This should be a SWITCHED connection, with it getting power with the ignition on only. (Speartech's mistake)

John also went on to say that the Camaro did not have this wire and that it is not needed to operate the alternator correctly. So... I'm going to try removing this wire from the connector and winding some electrical tape around it and loop it back into the wire loom to hide it. Hopefully this works... I'll be monitoring the whole deal with my multimeter and the car's voltage gauge. Dead batteries suck! :machine: