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Battery Drain


Tmta
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My 1975 02 had been running great until about a month ago.  Went out to start it and the battery was dead.  I ended up taking the car in to a shop and had the alternator tested, was not charging.  I was also told there was a drain coming off of the #5or #6 fuse circuit.  My reverse lights were not working so figured that could be the problem.  I replaced the reverse switch and confirm my transmission fluid was still full.  My battery is still draining. After I turn the car off a red "L" warnings light comes on the dash.   I first thought it had to do with battery being low, but even after putting in the new battery it came on.  Does that light indicate a low fluid level?  Would that warning light have a large enough pull to drain the battery in a short amount of time?


 


Tom

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Tom,

 

Stop and think about what is going on. You have a couple of different of issues going on. An alternator not charging and a battery drain are two different issues. 

 

First, the "L" warning light is your alternator charging light., not low level.  You have to remember, this is a 40 year old German car. Something has been lost in translation. Just like a modern day car, if the key is in the ignition in the on position without the engine running, the charging light should be on. Once the engine is running, the light should go off if the alternator is charging the battery. Once you turn the ignition off and take the key out, the light should go off. If the light stays on with the engine running, there is something wrong with your charging system. The "L" light is not draining your battery unless you take the key out of the ignition and it still stays on.

 

Second, a battery drain is is not necessarily related to a charging system not working. If your alternator is not charging, your battery will not recharge with the car running. If you replace the battery, you still need to find out why your alternator is not charging or else the new battery will go dead also. When I bought my car, the PO had replaced the alternator and voltage regulator and the battery was still going dead. After checking the charging system, I found that the alternator was not grounded. A wire from the alternator to the engine block fixed the problem. There is a procedure that you can do with an amp meter to find the fault in the charging system. Do a search in the FAQ's and you should find it.

 

Third, your reverse lights could be the drain or it could be something else. You could have a short somewhere or a switch staying on. Transmission fluid level has nothing to do with the problem on hand. Did you check the bulb for the reverse light? You need to find out if the voltage drain is coming from the #5 or the #6 fuse as they are for different systems. This will help narrow down your search.

 

The first thing I would do is check and fix the charging system and then find your voltage drain.

 

Good luck,

Peter

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Peter,

 

I fixed the reverse lights, the switch was bad. The L light stays on when the car is off and the key is out.  On my son's 66 mustang we had a problem with the battery dying and one of the problems was the alternator ground wire, it was attached to the wrong spot on the alternator.  I just looked on line to see if I could find a installation instructions for a Bosch AL89X alternator, which the shop installed.  I was hoping they did not ground it properly, but I could not find the instructions online.  I have to assume the shop checked the alternator after they installed it to ensure it was charging.  I will try to take some readings tonight with the voltmeter and see what I find.   

 

Tom 

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Peter,

 

I fixed the reverse lights, the switch was bad. The L light stays on when the car is off and the key is out.  On my son's 66 mustang we had a problem with the battery dying and one of the problems was the alternator ground wire, it was attached to the wrong spot on the alternator.  I just looked on line to see if I could find a installation instructions for a Bosch AL89X alternator, which the shop installed.  I was hoping they did not ground it properly, but I could not find the instructions online.  I have to assume the shop checked the alternator after they installed it to ensure it was charging.  I will try to take some readings tonight with the voltmeter and see what I find.   

 

Tom 

The "L" light should go off after you remove the key from the ignition. Could you have a bad ignition switch? Does it go of with the engine running?

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It does not turn off when i remove the key but does turn off when i start the car.  Peter, I pulled the alternator off today and it appears all the connection are good and correct.  I have the ground wire you described.  I even pulled that off to make sure none of the connectors came loose during the installation of the new alternator.  Could it be a bad alternator?

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Remember, you have two different issues. First, the battery wasn't charging and second, you had a battery drain. You had your alternator replaced at a shop and if they knew what they were doing, it should be charging now. But you still have a battery drain. Your "L" light goes off when you start the car, that is good. It means the alternator is charging the battery. When you turn the car off and take the key out of the ignition and the light stays on, that is bad. That is pointing to your battery drain.

 

Here's an easy test to make sure the alternator is charging. You will need a multimeter to check voltage. Put you alternator back in the car. With the car off, check the voltage across the battery posts. It should be a little over 12 volts. Start the engine and check the voltage again. It should go up to around 13.5 volts. If it does, you know that the alternator and charging system is working.

 

Now you have to find out why the light is staying on with the key out of the ignition. 

 

 

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  • 2 weeks later...

I finally got back to my problem.  Hopefully you guys are still around to read what i found.  I tested the volt. across the battery posts with the car running and found the volts to be 13.45ish, seems to be charging.  I turned the car off (still have the red light) and tested again and noticed that the volts were dropping.  I disconnected the voltage reg (which i have already replaced) and noticed the voltage drop stopped.  Then I began checking amps.  With the volt. reg still disconnected, i checked the amps from the neg. battery cable to neg post (cable off the battery).  I found there was .285 amp drop, with the three prong plug disconnected from alt. there was a .085 amp drop, and with single wire disconnected (three prong reconnected) there was a .079 amp drop.

 

I reconnected the volt reg and checked again.  With everything reconnected (volt reg, three prong plug, and single wire) the amp drop was 2.376, with the three prong disconnected (singe connected) it was .075 and single disconnected (three prong connected) it was .08 amps.

 

2.376 seems high?  Any thoughts?

 

Tom

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With the ignition off, the only way to get current flow involving the regulator is if the rectifier in the alternator has failed.

 

First, you want to make sure that the ignition is really "off". Turn the car off and remove the key from the ignition.

 

Check the voltage between either end of fuse 4 and the body. It should be zero. Confirm your body ground by checking the voltage on fuse 1 - it should be battery voltage.

 

If you have voltage on fuse 4, the first suspect is your ignition switch. You should be able to pull the green wire off the terminal on the back of the switch. Re-check the fuse 4 voltage at that point; if it's now zero, your ignition switch needs replacing.

 

If the green wire checks out at zero, try your "everything connected" current test with the large red wire removed from the alternator (be very careful with this wire - it's connected directly to the positive terminal of the battery - wrap the end in tape and make sure it doesn't touch anything).

If this stops the current drain, then you need to repair or replace the alternator. You can try just replacing the rectifier pack, or you can use this as an excuse to upgrade to a newer alternator with an integrated regulator.

 

HTH - the wiring diagram here should be your friend:

 

http://www.2002tii.org/diagrams/bmw2002-usa-1975.pdf

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+1 to what mikesmith said.  That should help you pin point your problem.

 

But I should add that when the key is removed from the ignition, check that it is in the "HALT" or stop position. I have seen in older worn american cars where the ignition key will slide out of the ignition with it still in the on position. 

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Take your current meter and measure the current you see between the green wire and the ignition switch terminal you removed it from - important, make sure you have the red lead from your meter on the switch and the black lead on the green wire.

This looks like the rectifier in your alternator is shot. You should see a negative current reading with the test above if that is the case.

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