speaker polarity with a meter?

I don't think anyone has invented that yet.  But the auto makers do use the same color wires on every like vehicle.  That info can be found here on this forum https://www.the12volt.com/installbay/vehicles.html

If you still insist on not trusting this you could always use a 9 volt battery and a single straw from a broom.  Push the straw through the grill till it touches the cone of the speaker and pop it with the battery,  straw pushes out of the door, speaker is in phase.  Straw remains where it was, the speaker was sucking in thus meaning you had it out of phase.