New Battery loosing charge alternator output at battery terminals when running = 14.3 V

Dear Joyce,
The "battery not charging" light actually will tell you many things, and that one light is affected by several parts of the car.
If your battery is new, then the light is telling you some other part of the charging system is failing or has failed.
The most common part is the alternator.
The alternator, or the voltage regulator which is built inside the alternator, can both fail, and the light is telling you.
Those need to be checked by a repair man. (mechanic)
If you have no corrosion on the battery terminal, or the wires, or inside the insulation of the wires, the alternator should be your problem.
God bless your efforts.

It isn't a good idea to disconnect the battery while it is running as the resulting voltage surge can damage electronics. Obviously if it isn't charging there won't be much of a surge...

Some alternators are mounted in rubber to cut noise and vibration. This type needs a ground wire which is sometimes forgotten during replacement and sometimes the ground wire just breaks.

A standard alternator only needs two or three wires and sometimes a ground wire. If the direct connection to the battery is good, the ignition light wire intact and working and if needed a battery sensing wire (though this wire isn't often needed in the last couple of decades) the alternator, if it is any good, will charge the battery at the regulated voltage of about 14.5.
If you are sure the alternator is a good one and it isn't charging the connecting wires must be at fault and need to be checked.

There is one other possibility and that applies only in the case of smart charging systems. If your car has a smart charging system the alternator will have several extra wires, usually plugged into the side of the machine.
The alternator works in a similar way to the standard unit except instruction from a separate control unit is capable of reducing or suspending charging. The smart charge black box talks with the engine management black box and charging is suspended during acceleration to cut fuel consumption or improve acceleration. A fault in the smart charge system can prevent the alternator charging.

Disconnecting the additional wiring will allow the alternator to perform its normal function without interruption. The ignition, charge or battery light is controlled by the black box and can do strange things that mean nothing when the smart charge is disconnected.

Not sure but I believe the GMC Yukon has an in line fuse in the charging line. If so the output of the alternator will not get to the battery. One way to check is to measure the voltage, when the engine is running. At above idle it should be over 13 volts. Then measure the battery voltage, it should be almost the same within 200 to 400 mVolts. If not the charging line is open. Also if the alternator charging terminal is the same as the battery (12 to 12.7V) while the engine is running, that again indicates the alternator internal regulator is bad. If you turn on the headlights with the engine running above idle and the alternator output drops over a volt or so, the alternator is bad. This measurement can be taken at the battery plus terminal or the alternator charging output.

Hi , you must check wiring from alternator to battery . And replace your battery terminals.

Removing either battery cable, thereby taking the battery out of the circuit, with the engine running can cause the alternator to charge full tilt and destroy sensitive micro volt (computer controlled) components; and I've seen wiring harnesses go up in flame from it. You may have a module problem.

Hi,

Check if the alternator output is 13 volts to 14 volts or when the engine runs try to disconnect the negative (- ) terminal from the battery, if it still runs your alternator is okay. Just to check if that new alternator works.
If the procedure that I have told you is working, the battery must be brought to the nearest battery center, they have a load tester that will definintely assess the battery's condition if it really good or needs to be replace.

Hope that charge up the problem!

Thanks for using Fixya!

Even a new battery will go dead if the car is running on the battery instead of the alternator.
Check alternator output.
First charge the battery up.
Then check voltage with a meter from Harbor Freight ($3).
Should be 12.5.
The start engine and rev it up.
Should go over 14.
But also clean and grease battery terminals, alternator terminals, and check engine ground strap.

Ok, i understand that you have replaced the alternator, but there seems to be a non charge state in this case. i recommend checking the charging system. use the procedure below to isolate this issue.

Wear protective eye wear and clothing and remove all jewelry when checking your battery and charging system. Jewelry is a good conductor of electricity and is not recommended. Most batteries wear out every 3 to 5 years and need to be replaced. Always replace your battery with an equal replacement battery to assure proper operation. Automotive batteries have a +positive terminal (red), - negative terminal (black). The battery in this illustration has a protective cover over the positive terminal to prevent short circuit in case of an accident. Electricity is stored in the battery and then supplied to the vehicle when the engine is not running. While the engine is running the vehicles alternator charges the battery for future use. (Note: never disconnect the battery while the engine is running. If the battery cable is disconnected from the battery a spark can be generated which can cause the battery to explode or a major electrical malfunction to occur.)

To check a battery surface voltage, remove the positive terminal protective cover. Connect the +positive side meter lead (red) to the positive side battery terminal. Connect the - negative (black) side meter lead to the negative battery terminal. With the vehicle not running and the car sitting over night the battery voltage should be between 12.5 and 12.8 volts.(You will need to use a voltmeter for this testing procedure)

The alternator is rotated by a drive belt driven by the vehicles engine while it is running. Electrical voltage and amperage are generated to recharge the battery and supply voltage to the electrical system of the car. The alternator is held in place with mounting bolts. There is a main electrical wire on the rear of the alternator that supplies voltage to a main voltage junction box. If your alternator is not charging properly, your battery will slowly drain down from operating all the electrical systems in your car and stop the car from running.(most non charge states will be the cause of a loose belt or a low tension rate, due to a mis-adjusted alternator. make sure you have enough tension in the belt for full rotation of the alt pulley)

Next, you will need to check the alternators output with the Amp meter.

Testing the amperage output of the alternator is good for measuring the amount (not the level) of voltage the alternator can produce. This test can be tricky because if the alternator is weak it can still show it as producing amperage. Which is good, but if the voltage is low, it will still allow the battery to go dead. To check the amperage output of an alternator an amp meter is needed. Once the meter is connected start the engine. Next turn on all electrical accessories and raise the engine idle to about 1200 RPM. The alternator should output the max amperage it was designed to produce. Example: a 90 amp alternator should output about 88 amps. Note: An alternator cannot sustain maximum output for long periods of time. If the alternator is forced to operate at maximum output it will overheat and fail. An alternator is designed to operate at max amperage output only for a reasonable amount of time.

((Connect the voltage meter lead the same way you would in a battery static voltage check, Start engine (do not drive) at engine idle the voltage should be between 13.6 to 14.3 volts. If not the alternator may need replacing.)))

could be your starter solenoid. check that.

clean battery terminals ,bring battery to be tested after charging, after reinstalling battery run car and test alternator output it should be a minimum of 13-14volts if it is under 13 replace alternator , use a voltmeter set on 12 volt 10 amp dc to check the wire to check is located on the back of the alternator covered with a rubber grommet of course hold negative wirw on volt meter to ground and touch red wire to big terminal on back of alternator while car is running should have 14 volts or at least 13 volts