To answer your question on what percentage of the current goes through what path, let's say your ten gauge ammeter line has a total resistance of .003 ohms, which is what one of the internet calculators says a three foot span of ten gauge wire has, and let's say your new parallel 12 gauge line has a resistance of .005 ohms. Now, the difference of .002 ohms is hardly anything, but it results in 62% of the current going through the ammeter and 38% going through the parallel line. Now, let's say something happens and that ammeter goes up to just .01 ohm (in one way, that's still not much). Now the current going through the ammeter will only be
half as much as the current going through the parallel line. Move the ammeter up to just 1 ohm of resistance and now the parallel line carries 99.5% of the current. I think I did that right...
