Voltage Regulator

Tiny
TROOPERKYLE
  • MEMBER
  • 1994 ISUZU TROOPER
  • 6 CYL
  • 4WD
  • MANUAL
  • 135,000 MILES
I've replaced the alternator twice in two years. I'm running a 75 amp. I've just installed: the charging indicator on the dash reads a bit above 12 volts. I've been told that the voltage regulator may be defective and burning out the alternator.

My question(s): Is this true? And if I'm to replace the voltage regulator, where is it located? Adjacent to the alternator?
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Sunday, April 18th, 2010 AT 1:26 PM

18 Replies

Tiny
BLUELIGHTNIN6
  • EXPERT
Your vehicle's alternator should be 75 amp rated and the voltage regulator is built into the alternator so that is not the cause . . are you putting any strain on the charging system such as extra lights, aftermarket sound etc..?

Verify the grounds are all clean/tight

Looks like you have a charge relay, it could be losing voltage there as well

Have you used a voltmeter to verify the accuracy of your dash gauge? You should test at the big charge wire on the rear of the alternator and at the battery to see if they are the same

Here's a guide on how to use a voltmeter

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Attached below is the wiring diagram for your charging system
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Friday, April 30th, 2010 AT 11:18 PM
Tiny
SHANNONL
  • MEMBER
  • 1994 ISUZU TROOPER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 211,000 MILES
I have a 1994 Isuzu Trooper I just recantly change my alternator and Im have problims it doesnt want to charge my battery I have 750 cold cranking amp battery in it is the battery to big or could it be the wires? The reason I had to change the alternater was the voltage regrulator went bad on it and it was spinking blowing my head lights and voltage meter went from 13 amps to 18 amps and I was wondering if the wiring was over heated that is causing the problims I have now with the new alternator? What do you suggest I should do?
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • EXPERT
Chances are the fuseable link is bad. It is between the alt and the battery. If it is bad, everything else can be good and the battery not charge.
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
KRISTPHILLIPS
  • MEMBER
  • 1994 ISUZU TROOPER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 198 MILES
What is the proper order of steps to the removal and reinstallation of the alternator.
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
BLUELIGHTNIN6
  • EXPERT
Start off by checking out the guide below on replacing an alternator, its not vehicle specific, but has some really good tips

https://www.2carpros.com/articles/how-to-replace-an-alternator

The instructions for your vehicle are attached below
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
RICHARD BEAMS
  • MEMBER
  • 1998 ISUZU TROOPER
  • 200,000 MILES
My vehicle will constantly drain my battery. I had the battery and alternator tested and both are good and the alternator is putting out only 12. Something volts.
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
CARADIODOC
  • EXPERT
The charging system must develop between 13.75 and 14.75 volts when the engine is running. If your mechanic said the system was okay, you may have an intermittent problem, and the testing was done while the problem was not occurring.

Does the drain occur when the vehicle sits overnight or while you are driving?
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
RICHARD BEAMS
  • MEMBER
While it is running.
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
KEN
  • ADMIN
The alternator is bad then, here is a guide to see what you are in for when changing it out for a new one.

https://www.2carpros.com/articles/how-to-replace-an-alternator

Please let us know what you find so it will help others.

Best, Ken
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
RICHARD BEAMS
  • MEMBER
I all ready put a new one on last week and it is still dies on me and wont charge my battery.
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
MARK ABBEY
  • MEMBER
  • 1997 ISUZU TROOPER
Electrical problem
1997 Isuzu Trooper 6 cyl Four Wheel Drive Automatic 150k miles

alt. Not charging replaced it and fine for 2 mounts and same thing while driving will suddenly not charge problem comes and goes was told the alt. Signal goes thru the park lock solonoid?
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
RASMATAZ
  • MEMBER
Check fuses C-8/C-10 if okay

I think you should have the alternator gain control circuit check out on the computer-see below


http://www.2carpros.com/forum/automotive_pictures/12900_trooper_alty_1.jpg

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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
CARADIODOC
  • EXPERT
If the system is not developing at least 13.75 volts with the engine running, how could the mechanic say the generator is okay? Did he perhaps bypass the voltage regulator, or, as I mentioned previously, could this be an intermittent problem? By far the most common cause of intermittent failure to charge is worn brushes inside the generator, but you would have solved that already by replacing the generator.

Does the "Battery" light on the dash turn on when you turn on the ignition switch? If it does not, check for a broken white / green wire going to the generator, or a blown 10-amp "C-10 Meter / Gauge" fuse in the fuse box behind the left kick panel. I can't tell what else that fuse feeds, but I suspect you'd have additional symptoms.

Next, check for 12 volts on the black / yellow wire at the generator. To be accurate, these voltages must be measured with everything plugged in and connected. Back-probe through the back of the connector next to each wire. You should find 12 volts on this wire when the ignition switch is on. If that is missing, check the 15-amp fuse, C-8, also behind the left kick panel.

Next, check the voltage on the white / blue wire at the generator. This circuit appears to be very similar to Chrysler's circuit which I am very familiar with. If this works the same way, you can expect to find between 4 - 11 volts. The lower the voltage, the larger the magnetic field is being created, and the more output current you should be getting. If you ground this wire, it will make the generator charge wide open. That is how we do the "full-load output current" test, and it could be what your mechanic did to verify the generator was okay. By grounding this wire, you're bypassing the voltage regulator, so that becomes suspect. Also, all generators are very inefficient at low speeds so you won't cause any damage if you do this test for just a few seconds. You DO risk causing more problems if you allow this to continue for an extended period of time, or especially if you raise engine speed. Proper procedure is to ground this wire for just a few seconds to verify whether battery voltage rises significantly. You can also turn on the head lights and watch them to see if they get brighter during the test.

My diagram also shows a double white wire at the generator. They are probably bolted to the output terminal on the back, and they will be pretty fat wires, ... I mean RATHER fat wires. You must always find the same voltage there as you do across the battery posts. If you find very high voltage on those wires, say 15.0 volts or more, while you find less than 12.6 at the battery, check for a blown 80-amp fuse in the fuse box under the hood. Fuses that large are often bolted in. The diagram only shows that something else feeds off that fuse on the same side as the generator's connection, so there will be other circuits that are dead if that fuse is blown, but they will work while the engine is running since they're being fed by the generator's output. Although the circuits will work, current won't be getting back to the battery to keep it charged. If that fuse IS bolted in, that's a good place to find an intermittent connection. Be sure both nuts are tight.

A second way to check that output circuit and fuse is to measure the voltage on the generator's output terminal, (double white wires), when the engine is off. You must find full battery voltage there. If the fuse is blown, you'll find 0.0 volts there.

If all these voltages are right, including you find battery voltage is between 13.75 to 14.75 volts with the engine running, there is one more way for the generator to let the battery run down. That is if one of the six diodes in the generator is defective. The only listing I found for your truck is a 75-amp generator. With a failed diode, all you will be able to get during the full-load output current test is exactly one-third of the generator's maximum rated current; in this case, 25 amps. That is not enough to meet the demands of the entire electrical system under all conditions. The battery will have to make up the difference until it slowly runs down over days or weeks. You need a professional load tester to measure full-load output current. It will also measure "ripple" voltage. All AC generators develop three-phase output current which is very efficient and results in very little voltage variation, which is "ripple". With a failed diode, one entire phase will be missing causing ripple voltage to be very high. Some testers that provide printouts list ripple as a voltage. I don't know what "normal" is because I always used a tester that used a bar graph to show relative voltage between "low" and "high". Regardless, it's that 25 amps that is the clue we're looking for. If all the voltages are okay at the generator's plug, have the charging system tested again, and find out the value of output current.
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
RICHARD BEAMS
  • MEMBER
The battery light does come on.
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
CARADIODOC
  • EXPERT
That's just the initial observation. Take the voltages readings right at the alternator.
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
KEN
  • ADMIN
Here is a guide to test the alternator yourself, please let us know.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

If it is not charging our team will give you a wiring diagrams to start testing wires.
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
ENADCL
  • MEMBER
  • 1996 ISUZU TROOPER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 21,100 MILES
The battery was replaced a few months ago but this morning when I went to start the car the power died, no lights nothing. A friend came over cleaned the battery cables and tightened everything up and it seemed to be fine. Tonight I went to start it the same thing happened. It appears to happen as soon as I turn the key. Before then I have a dome light but then as soon as I turn the ignitiion everything goes dead.

I am wondering if it could be a relay somewhere or something in the ignition? After I read a few more questions I also have had the key sticking like the steering wheel was locked but that was not the case.

Thank you for your time!
Carrie
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Monday, January 14th, 2019 AT 5:44 PM (Merged)
Tiny
KHLOW2008
  • EXPERT
Hi Carrie,

Thank you for the donation.

I believe the cause of your problem are the battery terminals. Check for tightness and cleanliness of contact. Some sanding down of the terminal should help.

Pull at the terminal cables and try to twist them around. If they move easily, the terminals are worn and you need to repair/replace them.
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Monday, January 14th, 2019 AT 5:44 PM (Merged)

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