Hi,

I have a 1997 E420 that has twice now drained the battery after sitting for ~ 2 weeks. If it is driven daily / every other day, I don't encounter any (apparent) problems.

I have searched the forums and followed the recommendations of disconnecting the -ve battery lead from the battery post and connecting an ammeter between the -ve lead and the -ve battery post. I see no current draw, AC or DC on the meter.

At this point, I suspect operator error on my part - am I just not capable of using an ammeter properly? I ask, because I expected that by putting an ammeter in series between the lead and battery post I would be creating a very low series resistance and things in the car would be powered up - i.e. dome light on, radio on, etc. but I get NADA. I am reasonably sure the ammeter is working correctly, and the test leads are good.

What am I doing wrong? Any pointers / suggestions would be greatly appreciated.

FWIW, I checked the fuses, all are good. The only obvious electrical issue is that one of the bulbs that illuminates the odometer / temperature display in the instrument cluster appears burnt out - only the right half of the display is illuminated.

TIA.

/alex

p.s. I should also add that there is no power antenna that could be trying to retract, and that I made sure (especially before the 2nd 2-week non-driving, that no interior lights / radio, etc. were left on) AND that the battery was replaced with a brand-new Mercedes one following the 1st incident.

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1997 E420

When I was troubleshooting my '86 BMW 635, I connected the ammeter (actually a multimeter set to the OHMs setting (Looks like a greek Omega) between the negative battery terminal and the negative battery post.

Are you saying that when you do this you show no current draw - even when you open a door or turn on the radio?

Are you sure that you have the proper range set for the meter? My electronic multimeter automatically adjusts the range (from 10s of Ohms to thousandths of Ohms), but if yours is an analog device - it may need to be manually set to the thousandths or hundredths of Ohms range in order for you to see any current draw.

Let us know if this helps - this troubleshooting shouldn't be this hard. Hopefully your meter is working.

Regards,
Troy
1995 E420

< >>

Current draw [ AMPS] on an OHM [ resistance ] setting ????

Most meters require you to move the red lead to another position/socket to measure amps. Also, there is a fuse to protect the meter from excess current, like a short, and it may need to be replaced.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Hi,

thanks for the replies so far - indeed the fuse in the ammeter is blown. Will replace that and then hopefully be on my way to the real problem. (Don't you just hate it when the stuff you are trying to use to get to the bottom of a problem itself has problems ;-()

/alex

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1997 E420

Thanks Arthur - Of course I meant Amps, not Ohms fopr measuring current. That's what I get for checking the messages at work - thinking of 2 things at once. My EE professor from college would have some harsh words for me.

Troy
1995 E420

It's simple. If you want to find your 'leak', so to speak, remove one fuse at a time, only the ones that have power when the key is off, put the probes on each contact and check for current flow.

If you have an autoranging ammeter, don't worry about the setting. If you have an analog meter, put the red lead on the battery or powered side and the negative on the other. Current will flow through the meter and give an indication. Proceed slowly and methodically and the answer will appear.

Check the trunk light first, the switch may be bad.

Good luck and report back.

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

If you try to measure amperage with the resistance (ohms) circuitry in your meter, you'll blow the fuse again. When using the resistance portion of the meter, the meter itself provides a minute voltage that it puts through the circuit being tested. The amount that this voltage drops reflects the amount of resistance in the circuit.

Using an instrument to detect battery drain requires that the user fully understands the capabilities (and limitations) of the measuring device. See if you can find the instructions for the meter and follow them. Remember, an electric clock will draw a small amount of current (as would the dome light if the door is open during testing).

Good luck with your troubleshooting.

Wes

Update (and more questions).

Got the ammeter working properly now.

When connecting it in series between the -ve battery lead and the -ve battery post, I read ~12mA DC current. That current remains CONSTANT regardless of which fuse I pull out. I pulled all the fuses, in turn, in the box next to the battery (under the rear seat) and in the box under the hood.

What am I missing here? What circuit exists in this car that isn't protected by a fuse? I may be grasping at straws, but it is possible that some wire may have bad insulation and is making contact to ground? I would expect that this would lead to a more "violent" short. (I would also have expected this to be a more frequently discussed topic on the boards if it were common). Any suggestions on where to start looking next?

Thanks in advance

/alex

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1997 E420

If you are reading the meter correctly, then the 12ma draw you saw is not the problem. That would only total 4a/h over two weeks time. not enough to kill a battery. Matbe something else is going on? My SDL is going dead sometimes and I suspect something is up with the alarm. Door lock wiring was butchered by a crappy paint shop on mine. 12ma is probably a clock or something like that.

12ma shouldn't be a concern. That 12 ma may very well be keeping your radio's memory hot as well the clock.

You might have your battery checked for capacity. It may be on its last legs.

Cheers,
Wes

Considering the complexity of the car you are working and your inexperience, I would strongly recommend making an appointment with a professionl. If you continue to poke and prod, you run the risk of wiping out THOUSANDS OF DOLLARS of delicate electronic components. If you were working on somethin from the 80s, I'd say go for it.

Good luck,

Peter

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Auto Zentral Ltd.

You will have to measure the current at the fuse. Remove each fuse and put the probes on each terminal. Measure the current.

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

Agree with Peter - have someone load test your battery.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Hi,

thanks for all the replies to date.

PETER, point well taken. I noticed your reg info says NorCal. Do you have any recommendations for a competent professional in the area? I am in San Ramon.

FWIW, I DID poke around some more, and need to correct my earlier observations.

I noticed the following consumers when measuring across the fuses - the fuse # refer to the fuse panel next to the battery, under the rear seat - the descriptions from the card in the fuse panel.

I would appreciate it if someone could render an opinion on whether these numbers are "normal" or "way off". I did these measurements several times, but, as seen in this very thread, I have been wrong before, so no offense is taken if you want to say "you obviously don't know what you are doing". I am not ready to give up just yet, though, so I would appreciate feedback.

#3: 50mA (!) - central control module / (entry / exit light), dome light, luggage compartment light (vanity mirror) - I DID verify that NONE of the bulbs in the circuits mentioned above are burned out

#8: 26mA - seat adjustment - front left

#9: 29mA - seat adjustment - front left (why 2 circuits?)

#13: 30mA - seat adjustment - front right

#14: 30mA - seat adjustment - front right

I am obviously puzzled by the above, particularly #8, #9 and #13, #14. How could a bunch of small DC motors use THIS MUCH stand-by current? However, the fact that all 4 circuits are very close to each other in terms of current consumption is also noteworthy.

Thanks in advance.

/alex

p.s. just to show more ignorance: to the person who posted 12mA DC draw ~ 4A / h (BobK?). Would you kindly share how to do this conversion?

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1997 E420