Current draw

[SoloSol]

After searching I still have some questions. Car is an 86 eta that I bought for a few hundred bux. It runs great but I am loosing juice. I put a new battery in it shortly ofter I got it thinking that it was just old and happend to die. Bad timing type thing. I put it in and everything was great, then I didnt drive it for a week or two. Get in it to drive one day and its dead. odd, but maybe I left the lights on or something.

Yesterday I have some time to work on it and cannot find anything left on. Doors were shut ect. So I got a draw on the battery. I looked around here and on other sites, but cannot find out exactly how to find it. Everyone is saying pull fuses. Okay thats clear enough. I understand that I need to pull the negative cable or the positive cable and hook up my meter to find the draw. Does it matter which terminal gets pulled? + or -?

Im good with a wrench but electronics get me. Which setting on my digital multimeter do I use? Is there a common place that I could start? This is my first BMW and dont know the car well enough to attack the problem without some guidence.



Thank you for your help

zach.

[jlevie]

Interpose the meter in the negative lead. That's safer in case a wire gets loose and contacts the car's body.

I don't know what the "book value" for parasitic draw is, but I'd guess on something in the 30-40ma range. Start with your meter on the highest range (say 10a) and work down from there.

[ScottL]

Most dime-store meters (RShack, Lowes, etc) won't measure more than a quarter of an amp. If you connect one of these in series with a 12V power lead, and there's a significant current draw, you'll blow the fuse in the meter. There are tricks to play with resistors and the like, but if you're not an electronics guy you might not want to mess with it.

Another trick is to place a test light (rather than a meter) in series with cable. If it lights up, you can then start pulling fuses until you identify the circuit that is leaking.

[jlevie]

The best meter to use is an autoranging DMM with a 10a capability. I happen prefer Fluke meters, but there are plenty of other choices.

[StereoInstaller1]

First, don't use a DMM to do your initial testing of a current draw, use a test light.

Bulbs are easier and cheaper to fix than your DMM.

Disconnect your negative terminal, connect one end of the testlight to the terminal and the other end to the batteries' negative terminal.

The test light will light up if there is a draw.

Make damn sure ALL the lightbulbs are off...glovebox, trunk, domelights, etc.

Now you can start pulling fuses or relays to find which circuit has a draw.

Soon as you figure out what is actually making the draw, look at the wiring diagram for your car to see what all that powers.

If you do not have a diagram, Massive Lee has found a great link to BMW electrical diagrams: http://wedophones.com/BMWManualsLead.htm

When you get to the point that the testlight has hardly any brightness, switch to the DMM, using "DCA" as your setting. You will likely need to change the lead positions, so look for the correct holes. My Fluke will do 20A, but it is automotive diagnostic type.

I use long wires so I can put the testlight on the windshield...makes it easier to see while working underhood.

Good luck!
Luke

[SoloSol]

Thank you so much. Ive got the day off and should be able to find this pretty quickly. :up:

[bolognablake]

I just recently bought a Craftsman Pro clamp meter, and I actually like it better than my Fluke meter. It did cost a little more than the fluke though.

[AndrewBird]

My Fluke will do 20A, but it is automotive diagnostic type.

Fluke 88?