I keep losing all electrical power. Replaced the alternator and battery but the test keeps coming back that the voltage regulator is bad. I am on a new alternator now that tested good out of the car but bad in it. It is putting out about 12.4 volts without any electronics on, then I turn on the A/C and headlights and it dropped to 11.9 volts. I am lost as to what else it may be...

the problem is in the voltage regulator
maximum voltage is controlled at 14.5 to 14.8 volts depending on whether the voltage regulator is in the ECM or not
but 14.8 would be max allowed any higher can damage the electronics of the vehicle including the ECM
take it to an accredited auto electrician, have it test and adjusted or the regulator replaced

For starters, it sounds like your battery can't produce enough amperage. Have it tested and replace if needed. Then see if things are better.

Bad voltage regulator. Usually built-into alternator.
Start car and unplug battery, if it dies your alternator is dead. Get new alternator. If car keeps running, get a voltmeter and check voltage coming through - should be higher than 12v but less than 18v. Any other number means your voltage regulator is dead, cheaper to get a new alternator.

if you replaced alternator 3 times , have you had your battery tested ? if battery is bad usually that will cause alternator to keep going bad . try having battery tested . might just need a battery

CHECK ALTERNATOR DRIVE BELT TENSION IF BELT LOOK LOOSE ADJUST DRIVE BELT TENSION.IF YOU HAVE AUTOMATIC BELT TENSIONER CHECK FOR FOR BROKEN BELT TENSIONER. IF DRIVE BELT LOOK OKAY.CHECK ALTERNATOR VOLTAGE OUT PUT AT BATTERY WHILE ENGINE IDLING.BATTERY VOLTAGE SHOULD BE 13.5 - 14.5 VOLTS. IF NOT ALTERNATOR FAULTY.FIRST CHECK ALTERNATOR FUSE AND CHECK ALTERNATOR POWER FEED WIRE AND VOLTAGE REGULATOR WIRES FOR DAMAGE OR LOOSE CONNECTIONS. FIRST TURN OFF RADIO BEFORE REMOVING NEGATIVE BATTERY CABLE TO KEEP FROM LOCKING OUT RADIO.

LOSING POWER WHEN RUNNING COULD BE LOOSE BATTERY CABLE.FAULTY ALTERNATOR.NOT CHARGING BATTERY.CHECK BATTERY VOLTAGE SHOULD BE 12.6 VOLTS.WITH ENGINE RUNNING ALTERNATOR POWER OUT PUT SHOULD BE 13.5 - 14.5 VOLTS WITH ENGINE RUNNING IF NOT ALTERNATOR BAD.CHECK ALTERNATOR BATTERY FEED WIRE CHECK ALTERNATOR VOLTAGE REGULATOR WIRES AND CHECK ALTERNATOR FUSE AND MAKE SURE DRIVE BELT NOT LOOSE.BESURE TURN OFF RADIO BEFORE REMOVING NEGATIVE BATTERY CABLE TO KEEP FROM LOSING RADIO CODE.

Test the alternator again to make sure it is putting out the correct voltage. Also if you have a bad connection on the battery and battery cables you can cause arcing and that can drain you battery and will also cause the car to lose electrical power and stall like you had happen. Buy a batter terminal cleaner at any auto parts store and give the terminals a good cleaning and then tighten them down so they dont move.

sounds to me like you have a bad voltage regulator. The voltage regulator will shut off the flow of juice to the battery if it exceeds a level, usually 14.5 volts. So if the alternator is over charging then the voltage regulator will shut off the flow to keep your battery form dying completely and having to be replaced. Now a days the regulator is located in the alternator.

that was your education for the day. :)

If they only tested the charge the alternator puts out and it passed they most likely bypassed the voltage regulator. If the voltage regulator is bad then you will still need a new alternator.
follow the link below and read the full field testing portion for a better explanation if you dont understand my explanation.

anything else? just post it :)

http://books.google.com/books?id=3q85p56_PxIC&pg=PA84&lpg=PA84&dq=test+voltage+regulator+inside+alternator&source=bl&ots=neLFU7USZK&sig=fmzJ2GjbxqULa9pU2UHylJahYS0&hl=en&ei=r9bySvXhNo2Xtge89omuAw&sa=X&oi=book_result&ct=result&resnum=5&ved=0CBIQ6AEwBA#v=onepage&q=test%20voltage%20regulator%20inside%20alternator&f=false

The battery light indicates insufficient voltage. I would recheck all the battery connections to be sure they are clean and tight. I would also have the alternator output tested, since the light will come on if the alternator is not providing sufficient voltage to keep the battery charged. Take the vehicle to an autoparts store and they will test the battery condition and alternator output for free. Sorry for your trouble and I hope this helped, Best wishes.

Here's the key parts of the electrical system.
Battery: the source of your electrical energy
Alternator: The charging source for the battery. Driven by the engines rotation via a fan belt
Regulator: tells the alternator when your battery needs to be charged and how much.
The Load: all of the devices that use the batteries energy

If you have replaced the battery 3 times we can rule out the battery as the problem
You had the alternator check and it passed. We can rule out the alternator
The load: It's fixed and for the most part you can control most of this with knobs on the dash
That leaves only the regulator. If the regulator is giving bad info to the alternator that could account for the problem.

Try this ( if you don't have a voltmeter, places like AutoZone can make these measurements)
Start the engine and measure the voltage at the output of the alternator. It should be about 13.5 to 14.0 volts. Then measure the voltage at the battery terminals. It should read the same as what you got at the alternator. If it's not,check the battery cables for clean bright connectors. Use a battery terminal brush to clean the. If this still doesn't help check the regulator.

Hope this helps

Good luck Loringh