Dwayne:
Remember that a digital voltmeter has an input impedance of
something like a
a million megohms; Your test light has an impedance of something like 40
ohms.
Hence, the voltmeter acts like an open circuit.
Even an old, clunky analog voltmeter looks like 100,000 ohms or
more. In some
cases it is impossible to diagnose a problem without first placing a load on
the
circuit while using a voltmeter, because of the miniscule load that the
voltmeter
represents.
Vance
---------------------------------------
The most likely way for the world to be destroyed, most experts agree, is
by accident. That's where we come in; we're computer professionals. We
cause accidents. - Nathaniel Borenstein
-----Original Message-----
From: Dwayne Cooper [mailto:dcooper@paciolan.com]
Sent: Sunday, April 20, 2003 9:39 PM
To: 6pack@autox.team.net
Subject: Chasing a short -- Resolution
Thanks to the help of many listers, I believe I've eliminated my battery
draining short. It looks like the culprit was the new GM alternator and the
cure was adding a diode to the circuit.
There was something odd about this that I still don't understand: I was
originally troubleshooting by testing voltage between the negative post and
ground with a voltmeter. What I found confusing was that when I removed the
alternator plug the voltage dropped from 12 to 10 volts -- not to zero.
Then I started testing with a light and the light reliably went out when the
plug was removed and testing afterwards with the voltmeter yielded no
voltage. Its almost as if there's a capacitor somewhere else in the circuit
that's storing the leaking current and the voltmeter doesn't draw it down,
but the light does.
At any rate, I've installed the diode and both my test light and voltmeter
show no current. I'm out of town for a week so the 6'll be sitting in the
garage with the battery connected and if it fires up next Saturday, this
problem will be a distant memory.
Dwayne
'74
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