Elictrical problem? Is this normal? - Team Camaro Tech
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post #1 of 5 (permalink) Old Jan 7th, 06, 04:47 PM Thread Starter
 
Join Date: Jan 2006
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Elictrical problem? Is this normal?

Hello everyone/anyone,
Iím in need of help.
I have a '71 camaro and I came across a dilemma.

Is it normal for me to get a negative current reading from the fuse block with the ignition off

I mean I'm getting 12V with the voltmeter connecting the red lead to the + side of the battery itself and the Black lead to the fuses on the fuse block (reverse polarity).

When the ignition is off The fuses flip from positive to negative

I'm not blowing fuses and when I turn the igniton on they become positive but I think this is rather odd since I believe that fuses being that they are positive current should be completely isolated from ground even with the ignition off.

Could someone maybe try this on their camaro?
Please help
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post #2 of 5 (permalink) Old Jan 7th, 06, 06:08 PM
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Join Date: Mar 2002
Location: Austin, TX, USA
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Re: Elictrical problem? Is this normal?

If you are reading current with the meter I think this is normal. Current flows into the black lead and out of the red lead. When you think about it, it isn't possible to get current flow into the battery unless something is able to charge it to a higher voltage.

I'm not sure what you are attempting to measure if you are reading current. Chances are, what your are reading are leakage currents bypassing the car wiring and flowing through your meter.

The ignition switch cuts of positive power to most circuits in the car. As a result, most of those circuits will still be connected to ground. Your meter is bypassing the ignition switch. It is unpredictable what you will see using a meter in this way. A volt meter has something like 10,000 ohms of input resistance. So anything connected to the circuit you are measuring which has a much lower resistance (say light bulbs for example - 100 ohms or so), your meter will show full system voltage with the ignition switch off.

You should probably be measuring voltage instead of current (perhaps you are). For example, if you measure the voltage between the battery (+) and a fuse, you should see nearly zero volts (or a few hundredths of a volt). If you see something in the thenth of a volt range or more, you will be observing voltage drops from potentially bad connections. This is a good way to track down a bad connection.

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post #3 of 5 (permalink) Old Jan 7th, 06, 09:43 PM Thread Starter
 
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Red face Re: Elictrical problem? Is this normal?

First of all I'd like to thank you for your cooperation
I really appreciate your feedback.

I understand what you mean.

I'm indeed trying measuring the voltage between the battery (+) and a fuse and I get 12V with the ignition switch off.

I'm trying to understand why the fuses act or become grounded when I turn off the switch.

please help
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post #4 of 5 (permalink) Old Jan 8th, 06, 06:17 AM
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Jim
 
Join Date: Dec 1999
Location: Yorkville, Illinois USA
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Re: Elictrical problem? Is this normal?

Take a lool at the new "electrical basics" sticky in electrical. The first 2 are up now, I hope to get part 3, measuring electricity, up today. I think these may help you.

P.S. I'm not sure why anyone would want or need to measure voltage at a fuse references to +12v.





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post #5 of 5 (permalink) Old Jan 8th, 06, 06:49 PM
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Scott
 
Join Date: Apr 2005
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Re: Elictrical problem? Is this normal?

Dnult is correct.

If for instance you are measuring voltage from B+ to your tail light fuse, there is still a path to ground through the light bulb filaments and you will read battery voltage on your voltmeter but the voltmeter will not allow enough current to flow to actually turn the bulbs on. If you were to run a jumper wire capable of carrying the full current the same way as you are hooking up the voltmeter, the lights would turn on.

If you power up the circuit (turn the lights on), the voltage reading should drop to near zero. This is an excellent way to test for excessive resistance in a high current (or any) circuit. It's called a voltage drop test. As a for instance: connect the positive probe of a voltmeter to the battery + terminal and the negative probe to the starter + terminal and crank the starter. If the voltmeter reads more than about 1V, the resistance is too high such as a faulty connection or the cable being too small to carry the required current. Furthermore, the problem is somewhere in the circuit between the voltmeter probes. You can move the probes closer and closer together and take more readings to isolate the exact problem.
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