Many moons ago I worked in an electronics test dept.,
Occasionally we'd have a bad batch of circuit boards come through where the etching was not great.There would be a fine 'hair' of copper shorting out between tracks.I used a current probe which was like a pen with a carbon tip - you would just follow the current path along the circuit tracks with the pen until you came to the bridge across the tracks.There was an audible alarm with an adjustable threshold for the size of current path you were tracing.
Unfortunately,I do not recall the manufacturer of this device as my memory is failing along with my eyesight.I bet Mr Google might have some ideas though if you type in "current tracer" or similar search phrases.Spell current correctly otherwise you will probably get links to raisins or other dried fruits.
:-)