Three days ago, july 14, 08. I replaced my alternator and battery due to my charge indicator lite coming on in my truck. Despite this, The charge indicator lite remains lit. I am perplexed by this. I have a brand new alternator and battery, So what could be preventing my NEW alternator from charging my battery.
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Sounds like you alternator might not be charging. If you can charge the battery and get the vehicle to a parts store, like an Oreilly's or Pep Boys, they will be able to test your charging system and determine your problem.
Does the car crank slowly, or the starter clicks when you attempt to start it? If the alternator or voltage regulator is bad, the battery would continue to lose energy and appear to be bad. Alternators need to be fed voltage since they don't have magnets to excite the windings. On my Volvo, sometimes the indicator lights don't come on when I turn the ignition on, before actually cranking the engine. When this happens, I know from experience that the battery won't charge. Do you get any dash lights showing a problem?
You can check the voltage at the battery when the engine is running; it should be well over 12 volts if charging.
If a trunk, glove compartment or interior light is on, that can run the battery down too.
If the battery light comes on while your are driving than the alternator is not charging. The battery light comes on to tell you there is a problem with the charging system not the battery.
It is normal for the light to come on when you turn the key to the run position and then it should go out shortly after the engine starts.
When the light is on check the voltage at the battery if you have less than 13 volts the alternator is not charging.
the battery might need charged. every battery you get even one a mechinc fits for you. you should always take it out and recharge it yourself overnight. some batteries have dead cells due to sitting so long not being used. the older a battery is the more likely that is. through time a battery loses its charge. it could be a defective cell not able to charge. as i had on my car 7 months ago. i got a new battery and it kept going flat. i had to jump start my car EVERY day. i got sick of it, took the battery back and got them to check it, it was a dead cell. your battery might have some power but not fully charged. try this and put it back in. if light comes back on, it could be just a light that never likes to ******* aitting there in your face all day.
the hum is probably the alternator on its way out and is not charging the battery but check ur belt and make sure not to loose if u drive to one of the local auto stores most of them [like advanced auto-auto zone ]can do a free test on both and advise if replacement or repair needed
if its not charging while running at14.5 volts or so you have a charging problem mabey no power to the alternator if its charging at 14.5 or so and the batery load tests good and its going dead over night you have a draw from some component in the system.
Find your fuse panel. Take a picture of it with your cell telephone. With the car off, with a volt meter, remove the fuses one at a time. Measure every slot to find out what is hot and what is not. Any Hot circuits should be examined closely to find out what is ON when the car is OFF.
Places to look ... light in the trunk??? is it on or off with the lid closed? Under the hood? Same. Do you have a radio that comes on with the key off??? GPS, you leave plugged in? Cell phone or other gadgetry you may have plugged in to the aux power supply? Any other lights? Parking lights for example? Security system? CB radio?
After you have checked these items, and if you find nothing, you may want to have your alternator examined. If you have a shorted diode in the alternator, the power may be draining back to ground through this shorted diode. You could perform this test yourself by unplugging or disconnecting the alternator during the periods when you are not driving the car. If this is the trouble, on day three, when you reconnect the alternator, two things you will note: 1) there will be a pretty big spark & 2) you will still have charge in the battery (evidenced by the spark)(there will be some spark no matter what ... but a big spark will mean a big drain). I have seen shorted diode problems fixed by inserting a toggle switch in the alternator power circuit. The alternator will still charge the battery when the switch is ON with the car running. When you stop the car, turn the switch off, power will not drain through the alternator to ground. Probably not the solution for your Mercedes. The real solution is to replace the alternator.
BTW - do you have a security system in your car? A thief proof radio? Check your owner's manual for precautions you should take before disconnecting your battery with regard to the anti theft features of your vehicle.
You say your battery is new and dead after three days. If fully charged on day one, and dead on day three, that means your battery has expended between 500 (economy battery) and 1000 (premimum battery) "amp hours" of power (500 amps / 72 hours = about 7 amps per hour going somewhere. (An 'amp hour' is one amp for one hour) Ohm's Law applies.
I hope you find your trouble and I hope I have given you a few leads. Thanks for allowing me to assist you with this problem this morning ... good luck.
This can be poor grounding of the engine and alternator and battery as there is a potential drop. It can also be due to a mismatch with high load when the charging voltage is not balanced.
So since the alternator was replaced the rectifier/regulator also can have a small leak which is producing the soft light which goes off when the headlight is swithced off. A test may not show this because the charge would be seen but the fault is a tiny ac leak into the system due to the weak regulator. It might fail in the long run or casue static in radio.