Grounded circuit troubleshooting

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If there is a voltage differential between the two pieces of metal touched with the probe wires, then a voltage differential will be displayed. Example:

1 wire is at 100 volts the other wire is at 300 volts

what do you think you will read between these wires if these wires are in an open circuit?

The answer is:

between eachother, 200 volts between100 volts and earth ground or neutral safety bus, 100 volts between 300 volts and earth ground or neutral safety bus, 300 volts

This has nothing at all to do with current. There can be zero current flowing in the wires, and you will still measure this voltage.

Amperes is the unit of measurement for current.

What if -both- wires are alive with 300 volts? What will you read?

ZERO VOLTS if you just put your probes on the two wires, each carrying

300 volts!

IOW, if you don't know what you're doing, DON'T DO IT.

Lg

Wow.....

Are you two fools for real?

It's an old 12 volt car with a short.....

What's he gonna do, blow a fuse? LOL!

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >

What he can do is melt a wire, or an entire wiring harness, allowing a lot of current to flow through it while trying to find a short.

At least, that's what I did when I was eighteen and stupid. (It did turn out, though, that the insulation was all turning to goo and I had to rewire the whole car anyway.)

--scott

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There's your answer *Wise Guy*

Lg =======================================================

Bob told me you're both.

"dontlookback" wrote

Dead short meaning you blow the fuse every time you turn on the lights?

As others have suggested, use a test light or buzzer, but wire it to *replace* the fuse that keeps blowing. That will keep the current down to a reasonable level, as it has to go through the test light before the short to ground.

Remove every bulb that the circuit runs (I've seen bulbs where the filament supports inside have fused, causing a short), and if the test light is still lit, move on to the wiring, looking for frayed connections, insulation that's rubbed off where it goes through bulkheads, etc.

Do not use an ammeter- use an Ohmmeter. These are part of what is called a VOM, or today more likely a digital multimeter. I don't know of any specific sites for using them, but I'll bet a good google search would find some. Also, many libraries have books on using such meters.

If I had posted the question I'd be pretty confused by now. So maybe go to the public library and get a book on car repair and look in the electical section. I have copies of second hand basic maintnenance and repair manuals, including the Dummies one, and they show how to look for electical problems.

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get a wiring diagram if possible to see what all is in that circuit.i assume the fuse box or booklet indicates the name for the fuse involved?things are not always what they seem.dead ends and befuddlement can originate in making wrong initial assumptions.

See this part here...: ================================================================ I have a 71 Opel GT with a dead short in the instrument panel lunination circuit. What is the best way to isolate the ground as it seems that everything is tied together into one big mess. Are there any free internet sites that explain basic ammeter use and trouble shooting of grounded circuits. My experiance with meter use is none and would like to learn more in this area. ================================================================

This OP has ZERO knowledge and/or experience with using a multimeter, yet he is intent on troubleshooting a low voltage HIGH CURRENT problem. Have you ever shorted the B+ on a fully charged battery to the Ground terminal?

Be sure to use a nice thick WRENCH because a good part of it is going to be welded, and another part of it vaporized, just before battery EXPLODES spewing hot acid everywhere.

Now that is what fuses are for, but they aren't worth a shit as you and I know, when circuits don't use them because of a short somewhere.

So we are talking about the potential of realeasing an Electrical Bomb here, and you want to f*ck around with nomenclature.

I told the OP stay away. Don't do it.

And you can go back to sleep.

Lg

Far and away the best advice given up to this point. Good job, MB.

Toyota MDT in MO

Dash lights are hardly "HIGH CURRENT."

As was mentioned by another, the OP merely needs to substitute a

12 volt bulb (#194 in a holder) in place of the fuse that keeps blowing, when the 12 volt bulb is no longer illuminated, he's found the short to ground.

You forgot high frequency and whether it's single phase of three phase... 8-)