I just installed a woofer in the 8" door spot & the woofer DIDN'T have polarity printed on it!
I found correct polarity by an old trick... tape a speaker wire to a AAA battery, pay attention to which wire is +/-. When you touch the +wire of the battery to the +terminal of the speaker, the cone will push out, away from the magnet.
This is actually how I found out for sure that the Metra harnesses were the incorrect polarity. I did the battery/speaker test and matched it up to the harness.