If you intend to use the original speaker wires there is an easy way to check their polarity. For eaxample, when you replace the rear speakers the wire harness that is attached to the factory speakers has a 1 and a 2 where the wires are inserted into the harness. Normally the 1 is + but just to make sure get a 1.5 volt battery and a couple pieces of wire. Disconnect the speaker from the harness, attach a wire to each end of the battery then touch the other ends to the terminal posts on the speaker. If the diaphragm pops out then you know you have the correct polarity. Then look at the wire harness and see which wire corresponds to the + post.