You could pretend that you're trying to identify one network cable in a bundle and use a tone generator and probe. Attach the tone generator to the conductors and then probe every nail. (image: fiberoptics4sale.com)
One surprising but useful trick is that the human body conducts the tone quite well. A person can put their fingertip on the tip of the probe, then use another fingertip (even on the opposite hand) to quickly brush across a bunch of bare terminals. That is (or was!) a routine trick for folks working on analog telephone systems. I'm told that once in a while one would drag a finger across a pair that just happened to be ringing at that moment (90 volts AC), or perhaps across a pair with a T1 data circuit (130 volts DC!) and that was a thrilling experience. But I digress.
This is just a slightly faster version of testing for continuity across each nail head. If you put a finger on the probe and with the other hand swipe a fingertip across each nail's head you should quickly learn whether any nail has conductivity to the electrical conductors, and in case one is found, you'd know exactly which nail and therefore the precise location of the fault to be repaired.
On the subject of testing for continuity between each conductor and each nail head: you could short all the conductors together, then test for continuity between the lot of them and each nail head. There's no need to test every nail head to each conductor separately.