Ignition condensers are not polarity sensitive. If you watch an oscilloscope pattern you'll see a condenser actually switch its polarity several times while it's discharging between the "points open" and "points close" portions of the pattern. That diminishing-amplitude sine wave is the condenser dissipating the voltage spike it initially absorbed to protect the points from arcing and transferring metal as they just barely came open. They will also usually work on 6 or 12 volt ignition systems without any issues.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!