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  #1  
Old 03-20-2007, 09:51 PM
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Battery drain/discharge...how do I find it?

My battery's got a little parasitic drain.

Battery charge: 12.6V

With everything off, neg. cable unplugged, draw between battery and cable: 11.3V No Amp reading.

Then, doing it again, I noticed the 11.3 wasn't a constant thing...sometimes, it would start at around 10.8 and slowly discharge down to 9.2 or so and then bump back up into the tens and back down again, back & forth...

Pulled fuses. With the #2 fuse removed, draw between battery and neg. cable goes down to .02V. This is a nonesential circuit, so I can use the car without it, the buzzer doesn't work (kind of nice, actually), the interior lights, etc.

I'm guessing it's something to do with the hatch area, roof light, maybe the antenna. This area was damaged in an accident. The hatch trim panel is missing. Is there supposed to be a light in the hatch itself? I have a dangling wire that reads current when metered across the two poles.

Now...I'm not much when it comes to electricity. So I'm not entirely sure how to check a circuit to find a short or what's causing the draw. I have a multimeter, which I probe around with, but I have to admit I don't entirely know what I'm doing. I'm not looking for continuity--if I'm, say checking the light, do I pull the bulb and read the voltage across the two leads?

Any help would be greatly appreciated! Thanks!

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  #2  
Old 03-20-2007, 10:15 PM
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Start to put all your fuses back in one at a time until you see the extra draw start. The last fuse you have put in willl be the circuit with a draw. Once identified you can continue on the hunt with a better knowledge of where to look.
There will also be good discussions in the archives as this kind of thing comes up often enough.
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  #3  
Old 03-21-2007, 12:10 AM
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I already figured out what circuit it's on: #2.

I'm just not sure how to figure out what on the circuit is causing the drain.

I was wrong about the buzzer, too. It's not on that circuit. I had just had it unplugged!
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  #4  
Old 03-21-2007, 12:31 AM
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Where is that darn buzzer?
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  #5  
Old 03-21-2007, 08:44 AM
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Could it be a trunk light staying on? Good luck finding it -- sounds like a pain!
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  #6  
Old 03-21-2007, 02:26 PM
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On operating your meter.......to check current draw(amps) you will need the meter connected in series like this 0-meter-0 Such as between the disconnected neg. cable and the battery. BTW, you will read supply voltage at the end of an open circuit, because a meter is applied in parallel when used in the voltage function. (not demeaning, I was just unclear from reading your post if you understood this or not)
From what I've gathered, it sounds like the electric antenna may be cycling. On your car, what all is listed on the fuse you removed?
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  #7  
Old 03-21-2007, 06:34 PM
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Marshall,
Using a VOLT meter in this way can be very miss leading. Sometimes there will be a drain indicated until all the circuits stabalize. Some times they need full battery power to do this which they can't get thrugh a volt meter. An amp meter is the correct instrument to use but most multi-meters don't do the job. You must have a meter that can read down to 50 miliamp but be able to handle up to 10 amps if needed. Most multi-meters can do one or the other but not both at the same time.
But, if you could tell us what your problem is maybe we can help. For instance, i assume that your battery goes dead. How long does it take? Overnight? 2 days? etc. Could it be a charging problem. Does it have an aftermarket radio in it.
Give us some clues and we will try to help. By the way, this is the type problems I work on every day.
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  #8  
Old 03-21-2007, 08:37 PM
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#2 fuse circuit (82 300td):

-clock (inoperative)
-trunk light (does a wagon have a hatch light? I so, mine is gone)
-diagnostic (?)
-roof light front & rear (rear doesn't work with hatch lift)
-hazard warning system
-warning monitor term.5 (?)
-autom. antenna (inoperative)
-switch-over valve seat back arrester (elektronik radio)
(? , missing commas?)

I'm surprised that the volt reading woulnd't be telling me something if the #2 fuse is the only circuit that gets a volt reading with the car off...

I have a multi-meter. Part of the dial is "DCA", which I've been assuming measures "DC Amps." The demarcations are: 200m, 20m, 2000u (that's the closest thing to that symbol--what is it? milliamps?), and 200u.

The amp setting doesn't register anything between the battery and negative cable.

The battery discharges fairly slowly, like maybe in a week (?) I've never really timed it from full charge to complete discharge--and it's been a while, I've been leaving the battery cable disconnected a lot. I do have an aftermarket radio. Maybe this has something to do with that last item on the above list: "switch-over valve seat back arrester (elektronik radio)" ?

I've unplugged the antenna, still get a volt reading.

...
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  #9  
Old 03-22-2007, 12:54 AM
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Your multimeter reads amps, (m=milli and u=micro) however, in order to read higher current readings, some multimeters have a separate jack with "10A". Also, polarity is very important when measuring amps. Many meters also have a fuse for protection when using in amperage mode, it may be blown if you exceeded the rating of your meter.

If it takes a week, I'm thinking that your battery may be going flat. The items you listed, including the radio which probably draws about 20mA for the memory, shouldn't draw the battery down that much. Also the radio memory draw does have a slight pulsation to it, I noticed this when working on mine.

Once you start it, what kind of voltage readings are you getting at the battery?
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Last edited by SD Blue; 03-23-2007 at 11:17 AM.
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  #10  
Old 03-22-2007, 10:45 PM
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After it discharged for the second time, I took it to Napa, they tested it & declared it good.

When I start the car, the voltage (If I remember right, is around 14...), so I think the alternator's fine.

I don't think the radio is on this circuit (#2), as I can operate the radio with the fuse out.

As far as the multimeter goes: Yep, you were right "SD Blue": the fuse is blown. No wonder I wasn't getting an amperage reading.

My meter does have a "10ADC" jack. As an electronics nimwit, I'm still unclear on what each setting measures as far as range goes. A 20m setting would measure up to 20milliamps? A 2000u setting up to 2000 microamps?
How do you decide which setting to put it on? I know this is multimeter 101, but I was in postmodern film theory class that day, so I missed out...
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  #11  
Old 03-22-2007, 10:58 PM
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Quote:
Originally Posted by burntcloth View Post
My meter does have a "10ADC" jack. As an electronics nimwit, I'm still unclear on what each setting measures as far as range goes. A 20m setting would measure up to 20milliamps? A 2000u setting up to 2000 microamps?
How do you decide which setting to put it on? I know this is multimeter 101, but I was in postmodern film theory class that day, so I missed out...
First, purchase a couple more fuses for the meter..........just in case you blow another one.

Then, set the meter on 200m. This will give you .2A full scale and will easily allow you to troubleshoot the system.

Make sure everything in the vehicle is off and the doors and trunk are closed.

Remove the negative battery cable and connect one lead of the meter to the battery negative post and the other lead of the meter to the cable. Now you'll read the discharge from the battery to the vehicle. Anything over 60ma (about 1/3 of full scale) is not acceptable.

If the needle immediately pegs.........you've got a more serious draw and you'll need to use a larger scale than 200m.

Remove each fuse until the meter is below 60m and preferably lower than 40m. That's the circuit that's the culprit. If you don't find the circuit, then the alternator is suspect. Remove the power wire from the alternator and see if the problem is eliminated.
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  #12  
Old 03-26-2007, 08:29 PM
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blown fuses

Ok, so I got the fuses for the multimeter, put 'em in, set the meter for "200m," disconnected neg. batt. cable, put leads of meter from terminal to cable, got a reading and promptly blew the fuse.

Replaced the fuse, then I tried to set the meter on the "10A" setting (& moved the meter leads), and didn't get a reading at all. "0.00" Nada. That's strange. The fuse wasn't blown (I don't think the 10A setting even uses the fuse, actually.). But why wouldn't I get a reading on this scale when it was blowing the "200m" scale ?
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  #13  
Old 03-27-2007, 12:53 AM
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Sounds like you are on the right tack -- divide and conqueror. Find the fused circut with the draw, then look at a wiring diagram and see what on that circuit could be causing the drain. Check those thigns out one by one. You can take guesses based on what the owners manual says is on that circuit, and you might even get it. However, owners manuals typically list only the "major appliances" on each circuit -- there are often lots of little things too.

As for your meter, you may have fried the 10A part of its internal circuitry, especially if it isn't fused. If so, get a 1-Ohm resistor (try Radio Shack or measure out a 1-Ohm length piece of wire) and measure the voltage drop across it (one lead to each side of the resistor) -- each volt means an amp of current.
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  #14  
Old 03-27-2007, 12:32 PM
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It could still be the battery!

I had a charging problem on my 87 300D...the local battery house told me it was the alternator....

I took it to the mechanic who has always worked on my 87 300D....

After scanning the battery with his fancy new scan tool, he put a new battery in it.

No problem after nearly a year.

Hope this helps....

the tenor man
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  #15  
Old 03-27-2007, 12:50 PM
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There was a guy on here who traced a mysterious draw like that down to his original Becker stereo. I know you already checked the antenna (first place I'd look), how about unplugging the stereo?

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