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  #1  
Old April 20th, 2016, 10:00 AM
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Mike Barnett
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So I installed a new alternator and now I'm having issues with the battery voltage gauge. It used to stay steady in one place, but now moves around depending on how fast I am driving. It actually pegs out when driving on the highway. When the truck isn't moving it stays steady just above midway on the gauge. Measured voltage goes up to about 16v when revving the engine. It's almost like there is a bad ground or something, but my understanding is that the alternator is grounded at the mounting. Is there a voltage regulator that keeps the battery from overcharging? I've expected the battery to be hot if it's getting too much juice, but that hasn't been the case. Any help appreciated, I'm supposed to drive to SCARR on Friday!
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  #2  
Old April 20th, 2016, 10:35 AM
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John B.
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Do not drive it any more until fixed. You will kill every piece of electronics in the vehicle. The voltage regulator is inside the alternator. The alternator sounds bad.
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  #3  
Old April 20th, 2016, 10:46 AM
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John B.
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The voltage regulator the the little bolt on unit with the ribs at the bottom. It have a spade connector. Make sure that is good.

Also does the battery ldiot light come on with the engine off and ignition on?
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  #4  
Old April 20th, 2016, 01:30 PM
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Mike Barnett
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Quote:
Originally Posted by Red90 View Post
Also does the battery ldiot light come on with the engine off and ignition on?
The idiot light does not come on with the engine off and the ignition on. What does that mean?
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  #5  
Old April 20th, 2016, 03:18 PM
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Robert Davis
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Quote:
Originally Posted by RiftRover View Post
The idiot light does not come on with the engine off and the ignition on. What does that mean?
The field wire is the small exciter wire.
This is suppose to be hooked to one side of the ignition warning light (that John asked about).
The other side of the ignition warning light is connected to positive that is switched on and off when the ignition switch is in the run or off position.
When the key is on the light will glow because the ignition side of the light bulb has power from the ignition switch and electrons flow through the bulb filament to the alternator field.
When the engine is started, the light bulb stops glowing because the alternator is producing (+) current and the electrons stop flowing (mostly) because the current is balanced on each side of the ignition warning light bulb.

If ant part of this circuit were grounded, it will short out the voltage regulator inside the alternator (again that John asks about).

Sometimes, but not always depending on where the short is, the light bulb filament can act like a fuse and protect the DC regulator by burning the warning light bulb filament out.

You need to do 3 things Mike:
1.) Follow John's advice and discontinue driving the vehicle as long as you are overcharging the battery, which will ruin it.
2.) Have the alternator checked and if defective (sure sounds like it) fixed or return it for warranty... (if it came from me you get 12 months).
3.) Inspect and fix your wiring because if your wiring is faulty, the next alternator you install will suffer the same fate as the one you have NOW.
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  #6  
Old April 20th, 2016, 09:23 PM
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I agree. Pull the alternator and have it checked out before anything.

As to the idiot light, depending on your era of truck and wiring, a functioning bulb may be required to get the alternator to turn on. Some have a parallel resistor to avoid that problem. Can't hurt to check. Disconnect the D+ (small) wire from the alternator and connect it to ground. Turn on the ignition and the light should come on. If not replace the bulb and check its wiring.
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  #7  
Old April 20th, 2016, 10:10 PM
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Quote:
Originally Posted by Red90 View Post
I agree. Pull the alternator and have it checked out before anything.

As to the idiot light, depending on your era of truck and wiring, a functioning bulb may be required to get the alternator to turn on. Some have a parallel resistor to avoid that problem. Can't hurt to check. Disconnect the D+ (small) wire from the alternator and connect it to ground. Turn on the ignition and the light should come on. If not replace the bulb and check its wiring.
I know from experience that leaving the exciter wire disconnected will not charge the battery
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  #8  
Old April 20th, 2016, 10:27 PM
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I'm not telling him to leave it disconnected.... I'm explaining how to test if the bulb is working or not.
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  #9  
Old April 20th, 2016, 11:40 PM
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Mike Barnett
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Bulb was working. I replaced the voltage regulator with a new one. The female connection on the alternator side was a really loose fit so I also tightened that up. Went for a drive on the highway and the gauge stayed steady right in the middle like it used to. Measured voltage at the battery is now a much more reasonable 14.4 bolts and only goes to 14.6 when revving the engine. I don't think there is an issue with wiring given that this issue only appeared with the new alternator.
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  #10  
Old April 21st, 2016, 12:19 AM
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Sounds good.
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