Massive parasitic current leak (4 amps!)

[Multibeemer]

Well, two more things to scratch off the list. I disconnected the connector going to the radiator fan switch - still getting 4.2 amps of current flow. Same thing when I disconnected the connector going to the (aftermarket) ipod connector.

As far as checking whether the alternator is the culprit, what's the best way to do that? Will disconnecting the connector going to it be sufficient?

Any other common causes of a leak this size that I should check, before I go through the tedious exercise of removing each fuse one at a time? Thanks.

[Hvacdude]

I had a '88 750il that the battery went low after a couple of days. I put a amp meter in line {in series} of the negative cable to the neg battery post and pulled each fuse one by one. When I pulled a fuse and lost the current draw, I checked all the devices wired into that circuit. Turns out it was the lock tumbler deicer. The switch that enabled it would stick. So put a amp meter on it and pull the fuses one by one and go from there. Check the "usual suspects" first, for sure.

[SMOKEY53]

I think trader4 made a good suggestion which would be to 'listen' to the car. As in, go for a drive, pull it into a garage at night and just listen to see if you can hear anything whirring away. Just remember these cars take up to 20mins to fully go to 'sleep', so if something persists beyond that.....

[TerminatorX5]

on the far wall in the trunk (remove spare tire) is another set of fuses. they are master fuses and great grand master fuse.... remove them one at the time, it will speed up the narrowing down the fuse tree...

[Multibeemer]

Hvacdude,

Yeah, that's the path I'm on. I've pretty much ruled out the prime suspects, so I guess it's time to start pulling fuses one by one. I've already pulled each of the ones in the cargo area because they're a lot easier to get to, but no luck - still getting over 4 amps.

I have a question about this whole sleep mode thing. I disconnected the negative cable this past Sunday and fully charged the battery, and have kept the cable disconnected ever since. I assume this is plenty of time for the car to have gone deep into sleep mode. So when I reconnect the cable to the negative battery terminal (with a 1 ohm resistor between the terminal and the cable, across which I'm measuring the voltage drop), am I "waking the car up" and creating an unintended but normal drain? I've assumed that since my drain is so massive, the difference between the current draw in sleep mode, and that when the system is "woken up" is in the noise, but am I making a mistake with this assumption? Thanks.

[TerminatorX5]

i think with such massive drain the car can't go to sleep mode

[snbx5]

as above, mine had a erratic current draw of nearly 4 amps. it took nearly a week in the garage with them pulling fuses one by one and leaving a tester on the battery which then had a printout of what times it spiked
The fault sounds identical to yours

[Multibeemer]

It looks like I found the source of the current leak, but the job is far from done. I pulled each fuse, one at a time, and when I got to fuse 27, a flow of only 40 mA was seen, so over a 100X reduction. It was 4+ amps after pulling each of the other fuses.

But my celebration was short lived when I found that fuse 27 protects not one, but three (3) circuits, as follows: Glove box light, windshield washer system, and passenger compartment/trunk lighting. None of these lights are on when the car is at rest. I suppose I could try disconnecting the windshield washer motor's connector - anybody know where it's located? Any other suggestions as to how to start hunting down the source of the huge current draw which apparently originates somewhere in one of these three circuits?

trader4: I read 4 amps (actually 4 volts dropped across a 1 ohm resister placed between the negative battery terminal and its cable) when I disconnect the negative battery cable from its terminal, and wait a good while (typically several hours). As stated above, this massive leak goes away only when I disconnect fuse 27, when it drops to what I understand to be pretty close to the normal residual draw that occurs when the car is in sleep mode.

[Multibeemer]

OK, a couple of new data points, neither particularly encouraging. After I posted last night's post, a little voice inside my head questioned whether I had read the scale on my voltmeter correctly, and sure enough, I was off by 10X - with fuse 27 removed, I'm getting a 400 mA draw (0.4V dropped across the 1 ohm resistor), not 40 mA, which would be 0.04V. So, while pulling fuse 27 does give a 10X reduction in draw from the 4+ amps I get with the fuse in, it's still nowhere near the normal baseline level of 30-40 mA or so.

Second, I removed the connector to the windshield washer pump after putting fuse 27 back, and the current draw is back up to over 4 amps, so that's another (inexpensive) thing to scratch off the list.

I have to confess to not understanding very well what's to be expected as far as current draw when the car is in its various modes. Doing the testing the way that I am, with the negative battery cable disconnected now for nearly a week, and measuring the voltage drop across a 1 ohm resistor placed in series between the negative battery terminal and its cable, what should I expect the current draw to be? What does it actually take to put the car totally "to sleep"? I would think that having the battery cable disconnected for nearly a week should do the trick, but as I said, this is an area I'm not very knowledgeable. Thanks in advance the the continued advice.

[upallnight]

You need to be in the car or else opening any of the doors will turn on one of the courtesy light and will wake the car up.