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I recently replaced my alternator after my car died however it is still not changing. The battery Is not very old and tests fine so I’m assuming it’s an electric issue. I’m not an expert so I was wondering if anyone had any insight on what could be wrong
 

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  1. first, when you turn the ignition on before starting the engine, does the ALT/BATT light on the dashboard light up? if that ligth doesn't come on, there's no D+ current, and the alternator won't work.
  2. if it does light up, now start the engine, does that ALT/BATT light go out ? if it stays on, something is wrong with the alternator.
  3. pretty much everything else requires a volt meter to test... borrow a digital multimeter if you don't have one, or get one, they are really cheap now.
  4. measure the battery voltage with the car switched off. if the battery is fully charged and has been resting an hour or so, you should see about 12.6 volts. start the car, and you should see at least 13.8 volts, if you, the battery should be charging.
  5. on the back side of the right hand spring tower, just forward of the battery, there's a 3 terminal connector block, 1 thin connector on the far right side, and a fat stud in the middle and left side (left vs right applies to the CAR, not to you as you face this from in front). ignition off, measure the voltage from that small stud to one of the ground bolts on top of the spring tower. should be 0 volts. turn ignition on without starting car, now you should read somethign around 5-9 volts at that smaller screw relative to ground. this is that same D+ circuit. there should be 2 not-very-fat wires going to that small screw, one comes from the dashboard 'battery' light, and the other goes to the D+ terminal on the actual alternator.
  6. with the car running, measure the DC voltage from the alternator body to the negative terminal of the battery, if that's more than about 0.1 volt, the alternator ground is poor.
 

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If you bought any alternator brand other than BOSCH you need to return it. It calls for the BOSCH AL165X but I believe the AL66X can also be used which is available at RockAuto.
 

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If you bought any alternator brand other than BOSCH you need to return it. It calls for the BOSCH AL165X but I believe the AL66X can also be used which is available at RockAuto.
Not true.

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You've always told me to only use OEM.
Again, not true Tech. I've told/suggested you not to use junk branded parts. Denso, Bosch etc are all top shelf. You may recall discussions of OVP relay's that sell for under $20 vs OE that go for about $60. There is a difference.

Seldom do these alternators fail. Most often, it is a voltage regulator problem.

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Realmikeyp -

When you say your car died, did it die while running or did it just not start one day?

If you can get a volt meter, verify that the non running voltage on the battery is on the order of about 12.6 volts. Then check to set if the voltage rises to something on the order of 13.6 to 14.2 volts after you start the car. If it does, the alternator is putting out. If it is putting out and the battery "tests" good, perhaps you have a parasitic current draw, either internal to the battery itself or through one of the external circuits in the car.
 

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Okay, let's all pile on now (sarcasm). LeftCoastGeek covered everything this newbie needs to know at this point. Let's not confuse things with bad information.
 

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in earlier i was so worry about my alternator.
i buy Bosch made in spain 90ah alternator and it works good 14.2 volt at first start. but after 2 hours ride with all electronic on, AC, head lights and everything, my ALT charging at 11.8 volt. and i try to search all of information about alternator charging. and it says the minimum voltage of alternator is 13 volt. if not, your alternator is faulty or bad. but finally i got info from professional G class mechanic, and he says 11.8 is normal and minimum is 11.2 volt.

and.... Sorry for my faulty grammar....
 

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A healthy charging system should provide 13.4 - 13.8v at the battery, at idle. Your mechanic is incorrect on the acceptable charging voltage. The likely suspect is your voltage regulator. Mounted on the back of the alternator by two screws.

Change it.

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Discussion Starter #12
Might sound stupid here but the old alternator and the the new one were both 1987 even though my car is an 89 the car ran fine on the old alternator for a while but 87 is 70 amps while 89 is 80. Could this be my problem
 

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Might sound stupid here but the old alternator and the the new one were both 1987 even though my car is an 89 the car ran fine on the old alternator for a while but 87 is 70 amps while 89 is 80. Could this be my problem
If the alternator isn't outputting over 14 volts as has been said before, it is bad. Having different amp ratings isn't your problem. The regulator is an inexpensive part, so if your alternator isn't charging, just replace it (the regulator)
 

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Discussion Starter #14
  1. first, when you turn the ignition on before starting the engine, does the ALT/BATT light on the dashboard light up? if that ligth doesn't come on, there's no D+ current, and the alternator won't work.
  2. if it does light up, now start the engine, does that ALT/BATT light go out ? if it stays on, something is wrong with the alternator.
  3. pretty much everything else requires a volt meter to test... borrow a digital multimeter if you don't have one, or get one, they are really cheap now.
  4. measure the battery voltage with the car switched off. if the battery is fully charged and has been resting an hour or so, you should see about 12.6 volts. start the car, and you should see at least 13.8 volts, if you, the battery should be charging.
  5. on the back side of the right hand spring tower, just forward of the battery, there's a 3 terminal connector block, 1 thin connector on the far right side, and a fat stud in the middle and left side (left vs right applies to the CAR, not to you as you face this from in front). ignition off, measure the voltage from that small stud to one of the ground bolts on top of the spring tower. should be 0 volts. turn ignition on without starting car, now you should read somethign around 5-9 volts at that smaller screw relative to ground. this is that same D+ circuit. there should be 2 not-very-fat wires going to that small screw, one comes from the dashboard 'battery' light, and the other goes to the D+ terminal on the actual alternator.
  6. with the car running, measure the DC voltage from the alternator body to the negative terminal of the battery, if that's more than about 0.1 volt, the alternator ground is poor.
Check the voltage between the alternator and the battery and it was 0.4 volts
 

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It was suggested you check the voltage at the battery with the car running and electric consumers turn on. 13.4-13.8 is acceptable. If less than that, it's a bad regulator. If it's reading in the high 14's, it is also bad (can cook the battery).

Report back

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Did you check continuity in the wiring from the alternator to the junction point prior to the battery ?
My 300CE wasn’t charging, every electrical component checked out and discovered problem in a wire that broke down inside the harness.
 

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say huh? that mechanic is on crack.

anything under 12V is a battery thats over 50% discharged... 11.2V is a battery thats nearly completely dead. a fully charged lead acid battery at rest (an hour or more after being taken off a charger, and left disconnected from any loads) is about 12.6-12.7V. it takes about 1.2V more than that to push a charge into the battery.

minimum alternator voltage to maintain charge on a lead acid battery is around 13.6-13.8V, some alternators and battery chargers will do a 14.2 ro 14.4V 'absorption phase' for an hour or two once the battery is fully charge before reverting to 13.6-13.8V holding voltage.
 

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Check the voltage between the alternator and the battery and it was 0.4 volts
whatm the grounds? ok, so that probably means your altenrator has a godo ground.

now what about the other 5-6 tests I enumerated? I didn't type all that out for the fun of it, thats what I go through when I'm testing a charging system..

any discrepancy, I've got ansers, I just didn't feel like trying to explain every possible failure up front, its a complex tree of problem/solution.
 

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say huh? that mechanic is on crack.

anything under 12V is a battery thats over 50% discharged... 11.2V is a battery thats nearly completely dead. a fully charged lead acid battery at rest (an hour or more after being taken off a charger, and left disconnected from any loads) is about 12.6-12.7V. it takes about 1.2V more than that to push a charge into the battery.

minimum alternator voltage to maintain charge on a lead acid battery is around 13.6-13.8V, some alternators and battery chargers will do a 14.2 ro 14.4V 'absorption phase' for an hour or two once the battery is fully charge before reverting to 13.6-13.8V holding voltage.
yes im not really sure about my mechanic says.
i think if my car never had a problem with that voltage (11.8) its ok for me now. but if i have a time, i want to figure out this problem.
but i just want to tell you my ALT is charging at 13.5 with all electricity loads, but only 10-15 minutes from first start. after 1-2 hours the voltage is slowly drop down untill 12-12.5 at idle with all electricity loads. i think thats a really confusing problem ever on my car. is it right thats a faulty voltage regulator? besause i see this behavior since i got the new ALT.

sorry for my bad grammar. i hope you all can understand and help me 😄
btw my car is G 300 not 300E. but i think both of them have the same engine. Thanks.
 
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