89 300e not charging - Mercedes-Benz Forum
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post #1 of 22 (permalink) Old 07-11-2019, 12:14 PM Thread Starter
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89 300e not charging

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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post #2 of 22 (permalink) Old 07-11-2019, 01:34 PM
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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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post #3 of 22 (permalink) Old 07-14-2019, 06:17 AM
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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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post #4 of 22 (permalink) Old 07-14-2019, 06:40 AM
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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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post #5 of 22 (permalink) Old 07-14-2019, 07:07 AM
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Not true.

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You've always told me to only use OEM.
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post #6 of 22 (permalink) Old 07-14-2019, 07:14 AM
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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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post #7 of 22 (permalink) Old 07-14-2019, 08:52 AM
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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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post #8 of 22 (permalink) Old 07-15-2019, 02:20 AM
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Did you check out post 2 -7 left coast geek parts no 1 and 2 ????? [ no light no charge ]
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post #9 of 22 (permalink) Old 07-15-2019, 01:30 PM
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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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post #10 of 22 (permalink) Old 07-17-2019, 12:55 AM
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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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