diagnosing a mystery current drain

David Pertuz davidpertuz at mindspring.com
Wed Nov 19 23:26:40 CST 2008

So....I hook my meter up in series with the ground terminal, and I get 
no current reading. Zero point zero zero. ?!??

I pull out various fuses (ignition off, key out) and check for current 
across the various fuse terminals, and I get no current. ?!?

Meter is on 10A circuit. I don't know how to verify that my meter is 
working correctly with the power end in the 10A post, but it works 
normally otherwise, so am assuming it works normally there too. Nothing 
handy I can hook it up to with a known current in it to check.

Battery has been fine now for a couple of days when not hooked up, so 
it's not the battery.

This stuff (electrical diagnostics) makes me feel like a total dumb*** 
but methodical thinking has at least gotten me somewhere over the years.

Other electrical:
-tacho doesn't work (rather, it works incorrectly), rest of cluster is fine.
-cranking during start has been rather week since late spring or so. I 
can't remember what may have happened or been done, if anything, that it 
went from a strong crank to a weak crank.
-I did have an unexpected-dead-car episode last year some time (I'd 
forgotten about it but my GF remembered)
-defroster and hazards work
-fog lamps do not work. I never use them, so I don't know how long this 
may have been the case. But I know they used to work.

I would really like to drive this car to Detroit this weekend. But I 
don't want to have to disconnect the battery all the time. Sigh.


wc701lists at bellsouth.net wrote:
> davidpertuz at mindspring.com wrote:
>> My G20 has been suffering from dead batteries recently, and while the 
>> initial investigation pointed to a bad battery, it now seems to be 
>> pointing to some unknown current draw when the car is off. The 
>> battery will go down to 3.x volts in about a day when in the car, but 
>> seems to be normal (so far - it's only been overnight) when out of 
>> the car. 
> Put your multi-tester on the highest DC current setting, and hook it 
> in *series* with a battery terminal.  A lot of people get his 
> wrong...  you need to disconnect a battery terminal and put one probe 
> of the tester on the battery, and one on the terminal.
> Ok, hopefully your tester did not just go up in smoke  ;)  They 
> usually have a 10A or higher setting and a fuse for just such a cause.
> If it's running down in a day, you're probably now reading a fraction 
> of an amp.  Now pull each fuse and look for changes in the reading.  
> When it drops way off, you've identified the circuit causing the problem.
>   -Wayne

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