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Subject: Mystery Battery drain compiled info Author: ambishop as Martin : member since December, 2003 : 3238 posts Posted on: 2005-01-13 21:46:01

Happened to me a couple of years ago. Could not pin-point the problem through the wiring system; and the battery mostly drained when playing the sound system in the beginning-then on a daily basis. Replaced the alternator and still had same problem.
Decided to replace the battery cables, and found the battery drain originated where the battery's negative ground cable was un-noticeably loose on the engine block.

I just went through a very similar problem. Except my battery would go dead in 24 hours.
It turned out that the field wire that goes to the coil via the light in the dash was shorting out somewhere and burning the dash light out. German charging systems will not work if the light is burned out. Try having an equivalent light put in a wire that you run direct from the connection on the alternator direct to the coil and see if that solves your problem.

If your power ant is not retracting all the way it can drain your battery also. This happened to me in my 86 E24 took me some time to find as not always the case. I cleaned mast and problem went away. A few months ago, I was told that there is a heater element in the driver's side key hole, which is activated immediately upon insertion of the key. Apparently, it can stay on all the time, which would drain the battery. On my 1988 M6 this was replaced once by the previous owner.

There have been postings here also of the glove box staying on after closing, so you might check that as well.

This is assuming that you have already checked your charging system and battery.

I agree with Pedro's. If that doesn't fix the problem, you could connect a voltmeter to the battery to measure the voltage drain. Then you could start removing one fuse at a time, when the voltage goes up, you have found the potential cause.

(I admit I've never tried this as I've not had this problem but I've read about it in past posts.)

if car is left sitting for a couple of days battery is dead but enough juice to power radio etc (needs a jump start) but will charge when driven then dead a few days latter (new battery)I am pulling fuse #27 when car is sitting . This fuse powers door locks, door heaters etc to see if this is where the drain is happening and will put back in while driving, will also clean all wires at battery. If this dosent work I will try fuse #21,interior lights etc.
I will post results in a couple of weeks.

I had the glove box problem also. Light always stayed on - and would drain a good battery (in cold weather) overnight. Put an ampmeter on the battery, between the negative cable and the negative post. Check your amps - they'll be around .3-.5 if the light is on. Pull the glove box fuse (# is in owners manual) and see if your current goes to zero. If yes - glove box light is your problem.

The best place to check for a draw on the electrical system is at the negative post on the battery. Disconnect the negative cable and check amp draw there. With a digital volt ohm meter, connect the black lead, or com. to the battery, and the red lead to the battery cable. Make sure your meter is set up for checking current and not voltage. Open the trunk to see if you get a reading to check to make sure you have things hooked up right. The trunk light should draw about 3 amps. The older the car the smaller the amp draw. An 89 should only have a 30 mAp draw. That is .03 of an amp, if you have a .40, which would be a 400 map draw, that is to much. That will drain a battery in a weeks time if the car just sits. New cars with all the computers just have a 50 mAp draw after everything has gone to sleep. My 85 has about a 30 mAp draw with the car turn off and everything shut down.


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• Mystery Battery drain compiled info - Martin 2005-01-13 21:46:01 (16732 views)
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