On most older coils the + primary terminal connects to both the primary and secondary windings. The primary windings are on the outside of the secondary windings and the primary windings go from the + terminal to the - terminal. The secondary windings inside of the primary windings go from the + terminal to the center coil wire hole. So when the primary windings circuit is opened the collasping induced magnetic voltage cuts thru the secondary windings and makes a very large high voltage spark in the secondary winding coming out of the coil terminal. So if hooked up backwards the voltage to the secondary winding would have to backtrack thru the primary windings to the + terminal and then thru the secondary windings. So the voltage to the secondary windings would be reduced by the resistance of the primary windings since it would go thru the primary windings and then the secondary windings causing lower voltage and amperage output. It would still run but as was stated will have a lower output and could cause many problems. The condenser just charges while the points are closed and helps the primary windings to colaspe as it keeps the point current from trying to arch and then helps induce voltage in the windings. Ron