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Re: High Volt/Low Volt

To: Roadster List <datsun-roadsters@autox.team.net>
Subject: Re: High Volt/Low Volt
From: Ronnie Day <rday@hot.rr.com>
Date: Mon, 30 Aug 2004 22:30:42 -0500
>Andrew Murphy:

> Did some work on the car this weekend which included replacing my old coil
> with an MSD blaster 2. When I took the car out for a test drive, I noticed a
> very high reading on the AMP gauge. 30+ reading.
> 
> Well, I immediately turned the car towards home, but before I could get
> there, the AMP gauge suddenly went to a low voltage reading. (About -5 on
> the gauge)
> 
> Now I have no dash lights, no turn signals, only the mechanical gauges and
> the clock are working and I have very dim lights.
> 
> Without a wiring diagram to go by, what should I look for first? Voltage
> regulator? Anyone who is planning to come to the barbecue on Monday, if you
> have a voltmeter please bring it along.

Andrew,

First don't confuse amperage (amps) with voltage. Amperage is a measurement
of current flow while voltage measures force. In other system terms amps is
like the number of gallons per hour of fuel flow or cubic feet per minute of
air flow while the voltage measurement is similar to fuel pressure when
expressed in pounds pounds per square inch.

The ammeter measures the direction and volume of current flow. It's not
terribly unusual to see a higher positive current flow when first running
the car after it's been sitting for some time or the battery's been pulled
down by something like prolonged cranking before the engine starts. However
30 amps is a bunch.

The 30+ amp positive reading followed by the -5 amp reading would lead me to
wonder if the regulator and/or alternator might be fried, the -5 amp reading
might indicate that the car was running strictly on the battery at that
point. Obviously not a good thing. I'm not sure what kind of current draw
you'd see with the engine alone running strictly off of the battery. In any
case I'd have both the alternator and regulator checked by competent people,
not just the counter jockey at the local Auto Zone, etc.

Hope this all helps a little,
Ron






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