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Old 04-22-2008, 01:25 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #1 (permalink)
DSM Wiseman

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Alternator Issues - Brake and battery light

I have seen a lot of threads about this, so I'm making a Tech Article.

If your car occasionally has both the battery and brake light come on for a few seconds and then goes away - keep reading.

As we all know the purpose of the alternator is keep the battery charged while you drive the car. Alternators are made up of 4 parts:
1) Rotor
2) Stator
3) Rectifiers or Diode pack/bridge
4) Voltage Regulator

ROTOR - The rotor is basically a magnet that loops around many copper wires around an iron core.

STATOR - The loops of wires around the core is the stator.

RECTIFIERS OR DIODE BRIDGE/PACK - An alternator provides AC current, while the car runs on DC current - rectifiers or a diode bridge/pack consists of several diodes (which allow one way electrical flow) and they convert AC current into DC.

VOLTAGE REGULATOR - Some cars have external voltage regulators, while our cars have internal voltage regulators. People assume that just because they get a constant 13.4v-14v reading that the alternator is working, this is not always the case. A voltage regulator adjusts the voltage when there is load. For example, if your car comes to a stop at a traffic light with the A/C on and the idle drops to 800 RPMs, the alternator still needs to put out 13.6-14volts to charge the battery. A voltage regulator ensures that the volts are kept between this range to charge the battery regardless of RPMs, load (A/C, lights, etc).

If you have the battery and brake lights on and it goes off in a few seconds - this means that your alternator (most probably the voltage regulator) is ABOUT TO DIE. If you keep driving your car and don't do anything about it, you'll have a dead alternator (could be a couple of days or could be a few months).

Now you say, "Well, I took my car to Autozone, they checked the alternator, I got 14 volts, there is nothing wrong with my alternator and something else is wrong.". IF YOUR ALTERNATOR HAS NOTHING WRONG WITH IT, THE BATTERY AND BRAKE LIGHTS WON'T COME ON.


1) Get an Autozone alternator (do some reading about how the quality is hit or miss) and plan on using their replacement warranty,

2) Go to Mitsubishi and get a rebuilt alternator (I paid $250 for mine) and NO, Mitsubishi does NOT make new alternators, all their alternators are rebuilt,

*** EDIT 05-22-09: Found out from my local dealership today that Mitsubishi only uses the alternator casing when they rebuild alternators, apparently all the electrical components in it are new. ***

3) Take your alternator out of your car, take it to a alternator repair shop and have them rebuild it and replace any parts that are failing or have failed,

4) Get on eBay and buy a high output alternator (if you have a big stereo system or lots of lights and a high load system),

5) Get a 100% new alternator, BOSCH makes these and last time I checked they sell for about $400-$450.

Feel free to PM me if you have any questions.


Last edited by DGajre777; 05-22-2009 at 11:37 AM. Reason: Added information on 05-22-09
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