Polarity makes no difference here.
Without knowing what aftermarket solenoid you have I can only guess -- but if there are two big terminals and one small one then it is possibly wired the same as the original and reproduction units.
The battery cable goes to one of the big terminals and the starter cable on the other. AFAIK is matters not which big terminal is used for each. The smaller (but somewhat large gauge) brown power feed goes on the same big terminal as the battery cable.
The wire from the start button (white w/ red tracer) goes on the small terminal of the solenoid.
But again, what you have may differ -- post a picture if in doubt.