Since the secondary winding resistance is so high, either low voltage terminal could be used. one or two ohms of primary resistance added to thousands of ohms in the secondary isn't going to make a measureable difference. Once, long ago, the secondary winding was grounded to the coil case, until somebody figured out the battery, ignition switch, and primary wiring would make a more reliable secondary ground than a possibly loose, dirty coil bracket. Yes, the high voltage actually travels through the primary to find a complete circuit!
Something that WILL make a big difference in performance is getting the coil polarity reversed. There's something about getting the primary winding in series with the secondary that makes an engine run really lousy!
Jerry
