Short circuit/battery drain

Brendan Daly · 08-31-2005, 12:53 PM

I been doing some fixing of my sons '87 325e. However there is one problem I have been unable to trace.
When the car is parked overnight the battery drains. I have checked at the battery and there is a 3amp drain. I have checked each fuse with my ammeter to see which circuit is the culprit, however no fuse socket shows any current drain. There was an old theft alarm system retrofitted ( but not working anymore) which I though might be the problem. I have removed it and all the wiring but still no luck. Still 3 amps drain.
Any ideas of what the problem might be or how I might pinpoint the location of the drain ?

Thanks
Brendan

Wayne 962 · Wayne 962's Garage

Hi there. With the ammeter connected, pull out all of the fuses and relays (sounds like you might have done this already). Does the drain still happen?

-Wayne

Brendan Daly · 09-02-2005, 05:52 AM

Wayne,
I did not pull out the relays and only pulled out the fuses one by one. Are you suggesting that I initially pull out all fuses and relays in the fuse box an then check for current flow at each fuse ?

I did remove the ignition relay alone at one point but the 3 amp drain current was still there.

Thanks for the response.

Brendan

Bear · 09-04-2005, 05:41 AM

Have you tried disconnecting the negative battery cable and hooking the AMP meter between the cable end and the post and then pulling fuses one at a time to get a drain of 50 AMP or less?

Bear · 09-04-2005, 05:43 AM

Have you tried disconnecting the negative battery cable and hooking the AMP meter between the cable end and the post and then pulling fuses one at a time to isolate the drain?

Brendan Daly · 09-06-2005, 06:15 AM

Bear,
The experiment I tried was to pull each fuse out, one by one, of it's fuse socket and measured current flow between the fuse terminals hoping to find a 3amp flow. I then replaced each fuse as I went along. However I did not find 3 amps flowing through any fuse socket.
I will try the experiment you suggest.
Thanks
Brendan

Brendan Daly · 12-05-2005, 04:47 PM

Wanted to let the forum know I finally found the short. Turns out it was in the radio antenna motor control. I suspect the problem is associated fact that the antenna does not fully return to the home position when the radio or engine is turned off. So the quick solution was to disconnect the plug to the antenna motor (the white one) and leave the antenna fully extended. Now the current draw is approx 50mAmp.
One of the reasons it took me so long to figure this out was bad debug technique and an faulty Amp meter. When I had a good meter and followed the directions outlined by "bear" of disconnecting the negative strap I quickly identifies the fuse and was able to follow the circuit diagram to the culprit. There is an old addage "measure twice, cut once" that applies here.
Thanks for the help.. great forum
Brendan