+ to the switch. - to the points. The coil will work wired backwards, but, not as well. The windings in the coil are insulated from the can outside. So it will not short out. The coil is wound in a manner that reversing the current flow may reduce the output voltage(efficency) . That is an "Engineer" convesation that we can avoid. The last conversation I got stuck in like that was about "hole flow". Look it up if you need to. Still makes my headake after 50 years.
