Battery drain

[jonmon6691]

I think my electrical system may be draining the battery while its off, how can I test this? Ammeter on the ground cable?

[ZombiE30]

yes, turn everything off and put it the ammeter across the positive cable. I think it works on either one, but you should get a better reading from the positive side.

Then, take fuses out one by one until it drops this current reading to O. Then you know what circuit it's in.

note: This doesn't mean, take fuse 1 out, then take fuse 1 and 2 out. This means, take 1 out, put 1 back, take 2 out etc.


ps-I have a buddy that teaches at Corvallis. The History of Music and Culture or some such thing.

[jonmon6691]

note: This doesn't mean, take fuse 1 out, then take fuse 1 and 2 out. This means, take 1 out, put 1 back, take 2 out etc.

I'm studying to be an EE, I figured that part out ;)

I'll check it out tomorrow, is something like this usually a non-essential short that's just consuming power?

[ZombiE30]

hard to say.....but yes. Otherwise you'd be having driveability issues as well.

also, make sure you have all the doors/trunk closed! It sucks trying to chase around a parasitic draw when you've got the damn door open (which draws current to the interior lights).

I'm sure you already knew that, it's just an easy mistake to make without even realizing.

[TrentW]

What is it about BMW's in general that they tend to draw the battery down after sitting for even a relatively short period of time?

[ZombiE30]

I've actually not had this problem on either e30.
(so far......:shifty)

[jonmon6691]

So my multimeter's amp setting is broken at the moment so I testes the voltage between each fuse and chasis ground. I don't know if this is any help but... 21-28 where 12.3 volts and 4-6 and 12 where 0.5 volts, everything else was zero.

[ZombiE30]

wow.....that sucks.

I'd try to borrow one that works, but here goes anyway:

fuse #4: turn signal, emergency flasher lights and active check control (the LED panel by the sunroof)
fuse #5: windshield wipers and washer
fuse #6: stop lights, cruise control, active check control, ABS, interior lighting
fuse #12: radio, power, speedometer and instruments, OBC, clock

So, 12 should always have some power to keep the memory from blanking out every time you turn off the car. It's possible that 4 and 6 should also for the active check control, but I doubt it. And 5 definitely only needs power when the key is running.

Now you need some wiring diagrams for these circuits so you can start finding connectors and narrowing where the issue is. ps-it's often AT a connector