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Ok I've replaced my alternator and my battery is strong but the battery idiot light stay on. The plug in connection to the alternator was in pretty rough shape , actually disinegrated when i was swapping the alternator so I replaced with new connectors. Fuses look fine. Does anyone have a suggestion on where to look next.
Thanks
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Check the voltage output at the alternator with a volt meter.
Does the light get dim or go out when you increase the engine RPM's?
I've had bad alternators right out of the box and had one that was rebuilt by a shop where the battery light would stay on until the engine speed increased.
GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
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Born 8/1981
Sequence #3975
Click here to see more pics of my Vette on CarDomain.
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Borgeson Steering Box
Born 8/1981
Sequence #3975
Click here to see more pics of my Vette on CarDomain.
Lifetime Member #26
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Duncanville, TX - USA
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
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Along with what Darryl said aboot checking actual voltage at the alt and battery, my questions is....did this light stay on BEFORE you changed the alt?
"New" don't mean it's any better than the old one...it's just cleaner.
Check your voltages first, then we can run down the idjit light and get if turned off. 
"New" don't mean it's any better than the old one...it's just cleaner.
Check your voltages first, then we can run down the idjit light and get if turned off. Joel Adams
C3VR Lifetime Member #56 
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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m
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Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.
Replaced as in "NEW" or Re-man? I've had bad re-man ones from the box as well. Had my O.E.M. one done at a small one man business. Great success, and less money than China.
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m
Ok I know it's been a while but I still haven't resolved this and now the car is not always starting. I am getting 12-14 amps at the alternator and 12 at the battery. I've had autozone check both also and the test out fine. They suggest replacing the voltage regulator but I don't see one. Isn't the voltage regulator internal on the alternator? I'm really lost.
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Voltage regulator is internal.
You should be getting around 13.75 volts (not Amps) at the battery. So you said the alternator was tested at Autozone and they were getting readings of 12-14 volts at the alternator. Something doesn't seem right. I don't trust those test machines at auto parts stores. I've taken alternators in and was told they were good when in fact they were not good. I would take the alternator down to a auto electric repair place that repairs starters and alternators, etc.
What does the voltage do when you turn on the headlights and heater fan?
How does the ground cable going from the battery to the crossmember under the car look?
And how does the ground cable from the engine to the frame on the underneath right side of the engine look?
GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
'69 "N11" Sidepipes
Borgeson Steering Box
Born 8/1981
Sequence #3975
Click here to see more pics of my Vette on CarDomain.
Lifetime Member #26
Borgeson Steering Box
Born 8/1981
Sequence #3975
Click here to see more pics of my Vette on CarDomain.
Lifetime Member #26
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The Autozone machine is okay for most checks, but not all.
You have the battery cable to the back of the alternator, then the smaller plug with two wires. The red one is ( or should be ) another battery source. You also have another small wire. This one starts at the ignition switch, and goes to the warning light, and then to the alternator regulator, which is inside the alternator. It feeds an ignition signal into the regulator to let it know it's time to turn on and go to work.
If the light comes on when the key is on engine off, it has a complete circuit, and grounds inside the regulator in the alternator. When the engine spins and the alternator starts to charge it puts power to this line. This creates a hot to both sides of the wire/bulb, and the light goes out due to equal voltage stopping current flow.
Unplug the small wire with the key off. Turn the key on, don't start the engine. If the alt light is on you have a wiring problem. If it is off, plug the connector back in. If the light comes on the circuit is fine. If it stays on when the car is started, you have an alternator/regulator problem.
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kstyer said:
The Autozone machine is okay for most checks, but not all.
You have the battery cable to the back of the alternator, then the smaller plug with two wires. The red one is ( or should be ) another battery source. You also have another small wire. This one starts at the ignition switch, and goes to the warning light, and then to the alternator regulator, which is inside the alternator. It feeds an ignition signal into the regulator to let it know it's time to turn on and go to work.
If the light comes on when the key is on engine off, it has a complete circuit, and grounds inside the regulator in the alternator. When the engine spins and the alternator starts to charge it puts power to this line. This creates a hot to both sides of the wire/bulb, and the light goes out due to equal voltage stopping current flow.
Unplug the small wire with the key off. Turn the key on, don't start the engine. If the alt light is on you have a wiring problem. If it is off, plug the connector back in. If the light comes on the circuit is fine. If it stays on when the car is started, you have an alternator/regulator problem.
P Ok I've unplugged the plug into the alt and turned the key and no light. When I plug it back in the light comes on. The alternator reads 14.5 volts and doesn't fluctuate when turning headlights on or turn signals. When driving the radio will shut off and the gauge lights will go out, I assume to conserve nessecary power but not sure. I finally was able to get under car and traced the positive and negative cables as best I could, at least until the Lh went into frame rail and from what I could see the cables looked ok. Not sure what to try next. Any ideas?
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its possible one of your battery cables is not good as well, been there and took a long time to figure it out. They may look good but that doesn't mean anything. Things will still work maybe not as well or maybe not all the time, it can be very frustrating. took us 6 months to figure that one out.
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How did you figure out the battery cables were bad?
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in Forum: C3 Electrical, Body and Interior
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