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Old 09-24-2016, 06:55 PM   #1
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12 volt electrical short

I have a 12 volt electrical short problem. I've narrowed it to 1 circuit because it keeps blowing fuses. In addition when I plug my converter in there is a 50 amp short circuit breaker that heats up to the point of opening and closing creating a fluctuation in power and lights.

I would like to trace this wire with a tone but I can't figure out how to connect the tester. On a 120v circuit I can hook the tone generator to both the white and black wires with power off and have a great tone. On the 12v panel where the fuse is blowing I can hook one lead to the black wire but all the white wires go to a common ground block and I can not get a tone.

So as long as I don't plug in my converter and leave the fuse out I think the system is stable. When my house batteries run down I have to plug in a battery charger.

Any suggestion on how to trace this short would be appreciated. Thanks

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Old 09-24-2016, 07:18 PM   #2
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Have you had the battery cables off, just before this problem ?

Make sure the cables are correct.

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Old 09-25-2016, 11:58 AM   #3
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Some tone testers get their power from the line being tested (assuming it is live), so probably only work on the type they are designed for (120vac, for example). Others may have a battery, or a choice of live vs low voltage (battery) mode.

In any case, you already know the circuit that is bad. The short is in that wire, or the device(s) on the wire. Disconnect the devices and see if the fuse still blows with power applied. If so, it's the wiring itself. If not, it's one of the devices. Should not be too hard to track it down.
Gary Brinck
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Old 09-25-2016, 08:58 PM   #4
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Should not be too hard to track it down without a tone generator. Start at the converter, and work your way back to the battery.
DaveB, Raleigh, NC
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Old 09-26-2016, 07:46 AM   #5
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Of the wire is shorted and blowing a fuse then the tone is being killed by same short.

All is not lost...

First locate devices supported by that fuse either by checking the build sheet or inventory of dead stuff.

Place tone on fused side of where fuse goes and also your tracer.

Disconnect harness plugs or devices until you hear the tone.

Another trick is using the "mili-ohm" method.

Here you get the best ohm meter you can find that can read very low resistances to a couple decimal points.

Then check resistance to ground at various points in the circuit.

Usually at where the supported devices are connected.

The resistance will be less the closer you get to it via change in wire resistance.

Also...has anything been done lately?

Mounting screws are great at locating wire bundles as well as slides when bundles come loose.
Tony & Lori
1989 Country Coach Savannah SE
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Old 09-26-2016, 05:18 PM   #6
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12 volt short

Thanks for all the help. I did figure out how to tone a single wire and traced it to where it goes into the ceiling but then toned it coming back out to 2 lights. The lights worked fine even though the wire is disconnected from the power. This is leaving me scratching my head again but tomorrow I'll disconnect the batteries and the 120v power.
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Old 09-27-2016, 08:08 AM   #7
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I works when not connected then either wrong fuse or a cross connection is in place.

a cross connection would blow both fuses though...

Tony & Lori
1989 Country Coach Savannah SE
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