Date: Mon, 24 Oct 2011 07:26:37 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: [WetWesties] Multimeter help UPDATE-77 Westy
In-Reply-To: <5A93887A235C48469C8ED6DB92606541@MainComputer>
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At 03:52 PM 10/22/2011, Courtney Hook wrote:
>OK, so something is def. not good here. I wasn't getting anywhere
>with the multimeter, so I tried the other method which someone
>forwarded to me, I put a 12v light between the negative cable and
>negative post with everything turned off. The light came on. This is
>supposed to indicate a current draw. I then proceeded to remove the
>fuses one by one to see which circuit the light went out on. It
>didn't go out at all. I even removed the backup, gas heater, and 2
>other 30 amp fuses on my Westy. Light still stayed on. I took off
>the positive cable and removed the red + wire to the VW diagnostic
>plug at the back thinking it might be grounding, along with the
>other .... The light still stayed on.
I'm assuming a typo here. Reading the last two sentences as written,
you have the battery pos connected to nothing, the battery neg
connected to chassis ground through a test light, and the light is
lit. That's not possible. Given that assumption, you can use
current tracking to find the leak.
Hook the battery back up, leave the fuses removed. Add a long wire
to your multimeter + lead and connect it to battery positive. Now
set the meter to the 200 mv or lower scale and start probing along
your still-live wires (with a sewing needle if necessary), following
the millivolt drops which will gradually increase along a particular
wire until you get to the fault. You will only find drops on wires
where current is flowing, so when you get to a branch point find the
branch where the readings continue to increase as you follow the wire out.
You'll need good contact on the meter probes, may need to polish them
to avoid odd/misleading readings.
If the "sneak current" is enough to light a test light bulb I think a
200 mv scale will probably let you trace it; but a more sensitive
meter would make it much easier as you wouldn't have to travel so far
along a wire to get a noticeable drop.
If the sneak current is 200 mA, then you'd get about a 2.5 mV drop
along a meter of 1.5 mm^2 wire (fat 16 ga), but would need four
meters of 6 mm^2 (fat 10 ga) wire to get the same drop. This would
be a lot easier to trace with a 20 mV scale where you could read
fractions of a millivolt. I have a meter with a four-digit display
that reads to .001 mV. You probably don't, but the more sensitive
meter you can find, the easier the job will be.
Yours,
David
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