Strange Electrical Problem - battery drain

[bmwe30mtech]

Hi guys,

Car is my 1989 325i convertible. The only after market item is an alarm, which seems be drawing about 20ma (which is fine).

My battery keeps going flat, relatively fast (takes less than a day), and I am having trouble tracing the fault. The battery is almost new, and was fine, however the constant drain now seems to have ruined it and it will not charge. I am now using another good battery, just for the tests. So far I have done the following:

-Put a multimeter in series between the battery negative and the negative chassis terminal. The drain is off the scale on the 200mA option, but does not register when the meter is set to 10A (which I can't work out).
- So I put a spare fog light in series in this location, and it lights brightly - I think this indicates that there is a decent drain.
- I then removed the fuses and relays one by one. Strange thing is, the fog light is still lit, and there is still a battery drain - with a totally empty fuse box.
- When I remove the small positive lead running from the battery positive terminal into the fuse box (the thicker of the two bolted to the circuit board by the allen key), the fog light goes out. I have checked this wire between the battery and the fuse box with the meter, and there is no short.
- If I turn on the ignition, the clock warning lights all light up, and the ICV buzzes - this is with no fuses or relays in - is this correct?
- I have checked that there is no short circuit between the chassis and this positive lead into the fuse box.
- When I first touch the leads onto the battery, the indicators momentarily light up - seems odd given that there are no fuses in, and I suspect the alarm has been wired in un-fused. Like I say though, unplugging the alarm only drops background drain by 20mA, and does not affect the fog light wired in series being lit. I have wired the same light in series on another car (which has a 210mA background drain - also not good!) and it does not light at all. This seems to suggest I have a short somewhere on my convertible causing this large draw.

In short, the strange things are that the drain is off the scale on the 200mA scale (on two different volt meters), but does not register on the 10A scale, but it is enough to light a fog lamp. There is still a drain enough to light the fog lamp despite the car having no fuses or relays in it.

Any suggestions from people who know E30 electrics well/brianmooore? Car has barely been driven for two years, and developed the fault in this time.

Thanks for any help

[pianist]

You do know that you need to relocate cables on multimeter to use 10A option? Just want to make sure you use multimeter in the right way no offence ;)

[bmwe30mtech]

Yes the cables are the correct way around in each instance! On 10A it fluctuates between showing 100mA and 0mA, but again doesn't explain why it is off the scale on 200mA setting.

Thanks

[Brianmoooore]

Chances are that the 10A range on your meter is fused and that this fuse has blown.
My first though was a duff alternator (diode failure), but that would stop the drain when the whole battery positive clamp is removed.
The red lead that is causing the drain goes to the fusebox and connects directly to the inner end of fuses 21 to 28 and to pin 30 of several of the relays. An unfused red wire also goes on from here to the ignition switch.
A relay that is stuck 'on' would cause a drain, but is unlikely, since whatever the relay controls would be permanently on.
Things that come on with the ignition switch are normal - none of these are fused.
You say the indicators light briefly when the battery is connected. This is something that is quite likely caused by the alarm, and could well be normal, or it could be an indication that the problem is an alarm/immobiliser (don't assume that you only have one - I came across one E30 that had three; all still fully connected, and all non working).
Your next step should be to remove the glovebox access panels, and the panel above the driver's knees, and check for anything spliced to the plain red.

[Quaser]

sounds like it could be something like the starter or alternator - try removing the wires that go to these one by one

[bmwe30mtech]

Thanks for the replies guys. I have spent today working on it, and I isolated the fault to the alarm system, which I have now removed. With the alarm removed, the fog light does not light up anymore. However, there was still a 300mA draw somewhere (not enough to light the fog light), and this turns out to be the illumination of the electric window switches - they don't turn off when the doors are shut. I have looked at the switches in the door shuts, and they both have the two wires onto the back of them.

Any idea how I work out why the window switches are permanently illuminated?


Many thanks