diagnosing a mystery current drain

davidpertuz at mindspring.com davidpertuz at mindspring.com
Tue Nov 18 12:27:58 CST 2008

Hmm, I hadn't thought of the defroster - it is a pretty big draw. I'm not sure I have what larry's saying straight, however - it pulls current all the time unless you disconnect it? That's the only way it makes sense to me, but I think larry was saying the opposite. 

Any other big current hitters that aren't obvious?

The car has been troouble-free, but I did have a dodgy alternator harness plug for a while that would cause out-of-normal-range fluctuation in alternator output, seemingly always (whenever I measured it, anyway) on the high side only. During this time by tacho started acting up and has not been right since - it would usually read rpm/2 and sometimes jer around, now it tends to sit around idle. Got a new harness pigtail fom a yard and the charging system problem was solved, but the tacho remains.

How much current do the wipers draw? My wipers quit last winter due to an ice jam, and I traced the problem to a burnt-out motor, which I have not gotten around to replacing yet because I can't get the damn harness connector off.

I was really surprised at going from 11.8 to 11.1 overnight and then all the way to 3.4 by the time I got home from work. Sitting on a table, battery on its own was 12.0 last night after a charge and 11.8 this morning, so it pretty clearly seems to be something on the car.


>> One quick question though: do your hazard lights work? Is the switch
>> ok? I've found in my cars that leaving that switch disconnected (or 
>> is it the rear defogger switch?) causes the battery to drain. When I 
>This sort of makes sense to me now... I think it's the defroster switch.  My 
>rear defroster doesn't work.  In the B14, the defroster goes through some box 
>tied to the keyless entry.  My car was broken into last year and the yokels 
>that fixed the car didn't fix the keyless entry properly.  I was just getting 
>to the point that I was going to diagnose and fix my rear defroster when I 
>got the new car so I never bothered.  The car mostly sees the track so I 
>don't really need the rear defroster.  But your comment now makes sense as to 
>why I've got an unknown draw and have to leave the car on a battery tender 
>now.  It didn't draw power nearly as fast as David's experiencing though.  If 
>the car was driven recently and a lot, it'd take 2 weeks to go dead.  If I 
>took it off the tender and drove 5 miles and let it sit, it'd be 4-5 days to 

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