There is a way to test speaker wiring and polarity without tracing wires:

Locate in the dash what you belive to be the + and - wire for a given speaker. Using an AA battery touch the +/- leads to either end of the battery. If you hear a pop (harmless) then the speaker wires are working for the speaker that popped. Now to check polarity, take the grill cover off the speaker and repeat. Look at the speaker while touching the leads to the battery. If the speaker cone pushes "out" towards you, then the wire touching the positive end of the battery is the positive lead. If the speaker cone "pulls" in, then you have the negative speaker lead touching the positve end of the battery.

On another note, it is possible that your front speaker wires are pinched in the doors, do a forum search on front speaker and you will find several threads on this. Not sure about your rear speakers, maybe they are blown, or maybe your head unit is no good. Do the AA battery test to see if you hear the pops.

 

Yup. I used this method all the time when at the stereo shop. Except I used a 9volt battery.