Technical Need Short & Broken Wire Finder Tester - where's the quality stuff? - Advice?

I have a loom short and want to spend some money on a good tool. I was hoping Fluke would have made something. Or OTC - they make a ton of little pocket light up probes but nothing for finding shorts (that I can find.)

This is all I could find and I just can't see someone specializing in electrical issues using stuff like this:

The Old School is to substitute a 10amp automatic circuit breaker for the fuse and use the analog D'Arsonval meter which jumps when over the wire and quits beyond the short. Modern sub electronics for the meter. Both put high loads on the circuit and spikes could damage electronics and sensors.

• Original Unit ($55)

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• Modern Version: ($125)

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Modern seems to fall into 2 choices:

• PowerProbe ECT 2000 ($112)
  

• $30-ish Chinese unit sold under dozens of names: ($24 Harbor Freight)
  

 

An inexpensive DMM should be all you need.

 

You can't locate the short or brake with a DMM - only identify the type of problem. NOTE: another problem is that DMM's w/continuity buzzers are so quiet, they cannot be heard in a shop environment. In fact, I just found my uncles old "pocket hearing aid" which I will use with headphones to be able to hear that weak tone.

 

I’m not talking about the buzzer thing. That’s actually a diode tester on real DMMs. If I put one lead at the end of one wire, the other at the other end. I look at ohms. If good and I suspect a short to ground I do the same thing, bout one end of the lead goes to ground. If I suspect two wires shorted together, same thing , but takes 4 iterations

 

Or are looking for something that can plug into one end of a wiring harness and tell you look 2.2 feet down and the green wire is bad? Not gonna happen

now I guess you could meg each wire out, but the ones that are bad still need to be replaced

if you suspect within your harness wires are shorted together, then meg wire to wire. Safest way is with the expensive digital meters, the wind up meggers can zap you quite well

 

I don't think I've ever encountered an electrical problem that couldn't be diagnosed with a test lite or a VOM .....

 

The way you find where the short is to put an alternating current on one end (and the short at the other end.) The alternating current in the wire will produce an electromagnetic field which can be detected by a "magnet on a spring" - do you have one of those cheap plastic ammeters you simply hold against the wire? Well when alternating, that needle will oscillate.

You follow the wire as long as need is oscillating, when it stops, you have reached the short.

It is easy to determine a wire is shorted. Finding the short is another matter.

As far as using a DMM, if you disconnect all loads on the circuit, you are left with a network of splices and multiple runs of wire. There might be 6 "ends" of that network. You easily demonstrate they all go to ground and you have a short. But your DMM is NOT going to tell you where the short is.

Since it seems that no one is familiar even with the Old School circuit breaker method (I wasn't a week ago!) , this may not be the best forum for latest diagnostic tech advice. I just thought that loom shorts are present in antiques and hot rods and people would be up to date with the latest methods. Where I live, local garages throw their hands up when trying to find shorts and broken wires. Everyone takes their trouble cases to Murray Auto Electric in Delmont who are so expert at this, they can charge by the hour to fix harness failures.

 

There is another level of testing which is not particularly useful with automotive since the wire runs have splices. But if they don't a Tektronix 1502b Metallic TDR Cable Tester sends a ping down a wire and can measure the length of that wire by the time for a reflected ping to return to the tester. This can be done with open and shorted terminations.

While useful when dealing with building wiring, a distance of 203' can get you close. But in a car, if you get 39 inches, it is difficult because the harness is irregular in shape and just how much distance is under the dash is unknown.

This job costs about $1500 used and obviously off the table. But I wouldn't put it past some auto electric specialist shop having one.

 

Nothing helpful to add , love your user name, hilarious movie.

 

I have trod in monsieurs bucket

 

So seem you answered your own question. You either have a background in the area, or are good with google

you’ll have to forgive my naive approach, it was 35 years ago when I went to school for electronics and around 10 years ago for industrial electronics, automobile wiring just doesn’t confuse me, like you’re making it out to be.


Best of luck in your quest

 

This, I worked as a mechanic for close to 20 years and taught high school auto mechanics for 13 years and there is very little testing on pre computer cars that you can't do with a simple test light and VOM plus maybe a continuity tester.
You have this many volts __ on one end of the wire and you have that many of volts _on the other end with a voltage drop somewhere in the middle. From there you find where the resistance is. Normally if your wire is shorted out it is going to blow fuses or kick a breaker out. If you disconnect it from the the power source and from the item it goes to and connect an ohm meter to one end or the other and the ground lead to a good ground you should be able to tell if that wire is going to ground somewhere in the middle.

All that fancy crap may be needed if you are working on high tech equipment but is rather a waste of money on our traditional hot rods.

Over the past 60 years I have found that the majority of wiring issues are either bad installation, wire rubbed though the insulation due to not being protected, bad ground connection or corroded connection. Correct volts at the battery but not enough volts getting here---- , Resistance somewhere in between, lets hunt the resistance.

I've gone out to help three different friends in the past 50 years who couldn't get their hot rod to crank when they got it all together who had too much paint under the ground strap. One actually stood there and cried that I had ruined his paint job when I took my Old Timer and scraped the spot to bare metal where the ground cable connected. He had even painted the whole bolt except the threads engine color so it would all match. It did crank right over when I was done. Another friend called me after he had replaced the battery, alternator and starter on is daily driver Grenada. I went out in the dark with my flashlight and my multimeter and it had 12V across the battery but no voltage when you grounded the meter on the engine. The ground cable bolt was seriously lose, I took it off, cleaned the area around the bolt real good, cleaned the end of the cable and the bolt and put it back together and it fired right up and worked perfect. 200+ dollars spent for a loose bolt.

 

Look for a company that rents high end electronic equipment and rent a time domain reflectometer, (TDR). You may even find one at an electronic swap meet or online electronic classified ads. We used them to find damage on RF cables when system test results were out of spec.


Sent from my iPad using The H.A.M.B. mobile app

 

What I can't wrap my head around is that outfits like Fluke, Mitchel, OTC, etc. do not appear to make one of these. Just found a $450 Snap-On and a $280 Matco.


I was just hoping to find someone who had something they liked.

 

To answer your question, Mac tools makes one, or at least used to make one. I bought one back about 30 years ago. Working on fire engines most of my working years, I encountered many problems with the electrical systems. Some of my looms would have near 75/100 wires in them and be two+ inches in diameter.
To solve your problem, locate the offending wires, disconnect them and add these wires to the out side of the loom and tie them up with zip ties. That way you do not destroy the loom.

Also if you have a bad wire inside of a good protected loom, with no outside damage, chances are at some time there was too much unprotected current going through that wire causing the insulation to melt and also could melt the insulation on a neighbor wire , causing a problem.




Bones

 

The "wire bypass" is a last resort. Problem is a collector car. BTW, there are a bunch of high tech loom building stuff that is pretty impressive (saw at a friend's shop.) Want to get more info on that too.

THERMAL IMAGING: I was wondering if a 20amp circuit, should be designed to handle 19 amps continuous, so if applying 18-19 amps to short, would the heat produced be enough to heat the loom enough to show up on FLIR (infrared thermal imaging)?

ALIEN TECHNOLOGY: SPATE: Stress Pattern Analysis aby Thermal Emission: Dynamic stress produces minute dynamic changes in temperature (compression higher, tension lower) and they have developed imaging that can detect that minute change in temperature. Soooooo... there is tech that would quickly see a loom starting to "heat up!" LOL​

 

Hook up a circuit breaker on that wire, if it has a short it will click, on and off and maybe give you time to find it after some time it may show up on a thermal imager! ?
That’s kinda why I mentioned adding the wire, instead of destroying the loom. You could possibly run the extra wire behind the loom where they are hidden.....maybe. Good luck, these kinda of problems are tough!






Bones

 

The problem is the loom is a bunch of tightly bundled wires with no place for heat to dissipate.. If the short is inside the loom, that 18-19 amps will produce localized heating at the point of the short. The resulting heat generated at his point will soon melt the insulation of the surrounding wires - causing your electrical problems to "snowball".

 

The only reason a wire melts in a loom is because too much current went through the wire . At some point in this cars life that circuit was unprotected when the short occurred causing heat. Had the circuit been properly protected by a fuse or circuit breaker, no damage would have occurred.
Adding a circuit breaker and putting current to this wire will not hurt the wire any further. But might let him find the problem.








Bones

 

Fluke and most other meter manufacturers don't sell these because most of their market knows they don't work well. Snap-on and Matco sells them to guys that don't know any better....

I spent 35 years in the electrical trade, and yes, tracking down a non-obvious short or broken wire is the bane of any troubleshooters existence. I've used these things more than a few times with very uneven results (including some of the high-$$$$ units), I can think of only once where one was particularly useful and that was finding a broken wire in a long (several hundred feet) run. If you can get a reading, I wouldn't expect accuracy of any better than +/- 12" at best. They generally don't work on shorts because the signal travels into whatever the wire is shorted to, not giving you a clear location. If you have an open, a signal generator type can work but keep in mind that an 'echo' can be induced in the adjoining wire/s if bundled tightly which can throw you off. This can be eliminated, but requires disconnecting both ends of all other wires in the bundle, bonding them together and grounding them.

There is no magic bullet for this....

 

Well , Steve we finally agree on something! Lol. I bought my Mac model thirty some years ago, tried to use it, didn’t work all that well for me, has just set in my tool box since then! I thought it was going to be the answer to my electrical troubles! Didn’t work that good for me. Just went back to my old was of search and fix!






Bones

 

I would argue that if the wire is fused at 20 amps, you can't fail the insulation along he length of the wire. But you would heat the wire up. But you could run any amp level 5, 10, 15 - if you want to be safe choose lower. But lower may not produce enough heat for thermal imaging.

Shorts are easier than opens because with shorts, you can get some current in the wire which an be detected. The Old School short detector was basically a "compass" you hold against the wire while a auto reset circuit breaker is used instead of the fuse. Around 1970 I bought a cheapo (probably cost $2) "Current Indicator" you held against the wire. There were 2 wire "grooves" on the back, 400 and 80 amps. As primitive as it was, it worked better than expected. Here are pics of an actual "short meter" and the "Current Indicator" (which has NO manufacturer stated on it - pure Brand X) - and also a pic of a 20 amp ATC resettable circuit breaker and also a higher quality "current indicator": The only thing I have against the Old School method is the application of a sizeable current to the wire. There should be "high impedance" methods where a "signal" is sent through the wire at very low amperage which still should be detectable - probably working more like an antenna than than a powerful EMF. NOTE: The short meter is at least 3 times as sensitive as the current meters shown - it is very twitchy and finds all kinds of fields on my cluttered computer desk.

 

Ive got one of those little red ones also! Like you stated works pertty good. The “ Mac” set up I bought years ago had a meter like the larger one you show there. It worked “ OK” but not as good as I had hoped.








Bones

 

>> I would argue that if the wire is fused at 20 amps, you can't fail the insulation along he length of the wire. But you would heat the wire up. But you could run any amp level 5, 10, 15 - if you want to be safe choose lower. But lower may not produce enough heat for thermal imaging.

20 Amps x 12 Volts = 240 Watts of heat. In normal operation, almost all of the heat is dissipated at the load - located at the far end of the wiring loom. The resistance of wire only produces a negligible amount of heat inside the loom.

If there is a short inside the loom, all 240 Watts are glowing at the point of contact. Testing at 10 Amps just reduces the heating to 120 Watts. If you have ever had to open a wiring loom after an internal wire burned off it's insulation, it is not unusual to find several wires with insulation melted and electrically joined together.

 

Good point.

Short inside loom usually means a wire was overloaded and melted through 2 layers of insulation which means damage has been done to loom.

But the most likely short is some sharp corner rubbed though the loom wrap and the insulation of the nearest wire.

How much heat in wire estimate: (like you said, all at short - so not so keen about a cycling 10 amp fuse for the Old School detector. However they seem to work without doing further damage - at least no one is talking about it.)

The real question is, if fuse eliminated, what would the steady state current be? It would be much more than 20 amps. Let's say 50 amps.

I believe the wire is 18ga which is 6.3 ohms per 1000 ft or .0063 ohms per ft.. I'm guessing about a 5' run so that is .03 ohms.

E = IR, so voltage drop along wire is 50 * .03 = 1.5 volts (75 watts) which leaves about 10 volts across short (500 watts).

 

So the wire you suspect is shorted to ground, I assume? And said wire is in a loom, right? I’m just try to get this right. Or do you suspect wires shorted together?

 

In order to repair the harness it will have to be opened . You'll see the problem when its opened. Why is it so important to pinpoint the exact location ? Open the damn thing & fix it .

 

You put 50 amps to a 14 gauge wire , shorted out and no fuse, direct hook up, make sure you have a fire extinguisher handy!








Bones

 

I suspect something rubbed through the harness wrap and shorted the nearest wire. The car was hit in the quarter and repair and the engine mounts are old and known for allowing engine to rock excessively. Twice the car blew the fuse when "getting on it.".

Hopefully today, I will test for continuity to ground when I perturb harness at all possible chasiss contact points. Problem is wiring goes behind engine (front wheel drive) and everything is very tight in the engine compartment.

 

I was thinking of maybe a 20/25 amp circuit breaker wired into that circuit, temporarily. I do not know the size of the offending wire. But, the circuit breaker will allow some current to enter the wire, before breaking and repeating. This should allow some heat to get into the wire/ loom and might be detectable with a temperature gun......or might not. I think a ten amp breaker would be too small to cause sufficient heat. But..... FYI... I have never tried this method, just a somewhat educated guess! Lol Good luck and keep us informed ,please.








Bones