I have two cars with recently developed dead shorts in the harness. 

Bot cars are fully assembled,  and the short appeared after a few miles. 

My normal method of finding a short is to start by disconnecting the components at the end of the circuit to tule out switches and bulbs and such. Then start at one end of the wire run and visually inspect the entirety of the harness inch by inch, disassembling and de-looming the harness as i go.

 

There HAS to be an easier way to do this that i haven't learned yet, or at least a more efficient way. 

 

What do yall do?

Mr_Asa
Mr_Asa UltraDork
1/4/21 5:29 p.m.

Is it completely blowing fuses?

Theoretically you could figure out the voltage drop for a particular gauge of wire, then see what voltage you're actually getting.  Should give you a rough distance of how long the "good" section is

In reply to Mr_Asa :

Yup. Both. One is a dome light in the truck, other is ac compressor in the neon. Both worked for a while after restoration. 

 

mjrj (Forum Supporter)
mjrj (Forum Supporter) Reader
1/4/21 6:19 p.m.

If it's a dead short on a meter and pops fuses, I like to check the circuit in sections if possible.  If there's a section of harness that is easily accessible I'd pull it apart there and split the circuit, that way you can tell which side the short is on.  After repairs I like to use a headlight bulb after checking the circuit with a multimeter to make sure the circuit can handle a load.

Stampie (FS)
Stampie (FS) GRM+ Memberand MegaDork
1/4/21 6:25 p.m.

Inductive DC voltage detector?  BRB gotta see if that's a thing.

It is! Amazon Link

So in theory you can start at the voltage source and follow along the wire until the voltage disappears.  That's the general area your short is.  You might have to put a load like a test light in series so that you don't blow a fuse.

TGMF
TGMF HalfDork
1/4/21 6:39 p.m.

Replace fuse with a small light bulb, something like a 168 bulb works well. It won't allow enough current to smoke anything.  A dead short to ground will illuminate the bulb. Start disconnecting circuits tied to that fuse. Light will go out when you disconnect the offending circuit. 

Brett_Murphy (Ex-Patrón)
Brett_Murphy (Ex-Patrón) GRM+ Memberand MegaDork
1/4/21 7:52 p.m.

If you figure this out, Michael, remember us little people when you're filthy rich.

Karacticus
Karacticus GRM+ Memberand Dork
1/4/21 8:14 p.m.

If you can get it to carry the current long enough, an infrared thermometer might catch it.

Actually, if you can get it to carry enough current long enough, the fire will tell you. laugh

Olemiss540
Olemiss540 Reader
1/4/21 8:22 p.m.
Karacticus said:

Actually, if you can get it to carry enough current long enough, the fire will tell you. laugh

Yes. When in doubt, short ALL circuits and start over. This is typically my approach wrt electrical circuits.

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
1/4/21 8:22 p.m.

I like using a headlight bulb or a washer fluid pump.

 

You can see a headlight bulb is on even if it's not in your direct field of vision, and washer fluid pumps (or the rattlebox style fuel pumps) are pretty audible, so yo ucan hear it if you're upside down with your head in the footwell reaching up behind the dash and wiggling harnesses around.

 

 

I disconnect everything from the circuit, refuse and see if it blows. If still shorted I run a new wire and abandon the wire in the loom. If it doesn't blow I add back everything on the circuit one at a time until it blows to identify the guilty item.

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