diagnosing a mystery current drain

Lawrence Weeks lweeks at anabasis.net
Tue Nov 18 14:05:41 CST 2008

On Tue, Nov 18, 2008 at 12:27 PM,  <davidpertuz at mindspring.com> wrote:

> 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.

Yes, the opposite. I've seen this in more than one of our cars (and by
our I mean the original Sentra/NX line). If you have the switches from
the center console disconnected, the battery drains quickly. Never
really looked into why. Probably the wiring diagram would provide some

> Got a new harness pigtail fom a yard and the charging system problem was solved, but the tacho remains.

That's not good. Hopefully it is the tach itself. It is driven by the
ECU, which gets the data from the crank angle sensor. I once had a car
(mid 80s Sentra) with tach issues, and it was the crank angle sensor
that was bad.

> 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.

You sure about that? Anybody else? Should the battery drop by .2 V
overnight with no load at all?

And as Jim wrote, I'd check the fuses for current draw. Most things
should have no draw whatsoever if the ignition is off. Check the
wiring diagrams.

Lawrence Weeks                                    lweeks at anabasis.net
Anabasis Consulting Ltd

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