Check with an ohm meter. If shorted it's bad. If it shows ohm meter increasing let it build, then reverse leads and it should drop back to zero and then build again. If so chances are fairly good that it's ok, unless it fails after operating awhile. If it shows open it's no good.
Only sure test is to replace with a known good one. New does not mean it's good.
Condenser doesn't care if system is 6 or 12 volt and doesn't care if positive or negative ground.
A good auto parts should be able to cross reference one to your tractor or engine.