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Is there an easy way to find a short or open circuit in a car? Answered

I am trying to find a open or short circuit that is on a wire which is in a harness with other wires, on a 1986 Mazda B2000 truck. With so many of you having expertise in electronics, I thought here would be a good place to post my question. Does anyone have any suggestions how to find this open or short-circuit?

I am open to the idea of getting a short-circuit-finder. Though I am not sure what features I should look for if I decide to get one. Does anyone have any suggestions?

a) Does anyone know if these work well?

b) What features should I look for If I get one?

c) Do you have any other on a short circuit finder? type, manufacturer, model etc

Below is a link to a site that uses a short circuit finder to find a short circuit, and has information on using one: http://inliners.org/tech/tech6.html

Below is a link to a site that tells about how a tone generator is used to find a short circuit, in a home environment (I think this is how most short circuit finders work): http://askville.amazon.com/tone-gene...uestId=5912724

I found some links that seem to show that it is possible to make a signal generator and tracer, but the pages with the schematics would not load. A list of tools with links to tools and their schematics

Circuit tracer (neither of these would not load 4-3-09 kept getting message "the Connection was reset."):
should have schematic:
and the signal generator:

A little paranoid voice thinks this Instructable has some clues to the solution: How to prevent thefts steal your motorcycle for less than US$ 2

Thank-you in advance,



10 years ago

I assume that you find the battery draining too fast? I'm thinking of pulling all the fuses out and stringing a 12V lamp in their place one at a time. If a fused circuit lights the lamp when it shouldn't be drawing power you've got a problem there.



Reply 10 years ago

No, none of that. I think I know what line/circuit the short is on. Though it seems to be inside an harness with other wires. So it seems I may need an open/short circuit detector to find it. Do you know of any good open/short detectors?


Reply 7 weeks ago

Get a portable small handy radio .
Turn it on on AM . Tune radio frequency on where there is no station but where you can hear a slight hum or noise keep it there ...
Turn the ignition on . Trace the harness with the radio. Where there is a short you gonna hear a noise from a radio. Open the harness on that spot . Inspect wires. Replace the wire. Job well done.


Reply 10 years ago

mm, can't a multimeter be used? Otherwise not too sure, sorry L


3 years ago

I had a b2000. think it was earlier model. what is not working?


4 years ago

If it is a short between two different wires it is usually easier to add two new wires to the harness (if accessible that is).
If the short is between the wire and ground it might pay off to check everything that is connected to it first - in many cases the "short" is actually a failing light fitting or similar (some people even manage to put break lights in the wrong way messing all up).
For a one time fault finding job like this you can also contact some of your local sparkies and ask them if you could borrow a short finder for a day.
Asking nicely might even get you a freebie.

While I was still working as an electronics technician in the field we had a little audio generator that worked on a single wire (the other could be used for a ground connection for very long cables though).
They work on the basics of a very weak radio sender.
With the receiver you go close to the wire in question and ajust the sensitivity so you just get a clear signal.
When following the wire now the signal will drop out or become "noisy" when you reach a problematic area.
These devices were quite expensive at the time and our boss rented them out to other people and companies for one off jobs.


4 years ago

try putting in a low amp circuit breaker. Or a flasher into the circuit. Then follow the wire with a magnetic compass. Each time the circuit energizes the compass will sweep. When you find the open or short the compass don't sweep