There is no way to measure positive/negative on speaker wires. Positive should be marked, but don't trust FR's installation. You could measure for continuity with a multimeter (Ohm) but far easier is to connect the speakers, don't fully screw them in yet, and connect bluetooth your phone to the stereo, and listen to the following youtube video: https://youtu.be/lsddq6yR0DY
After the left and right test, you will hear the phase test, which will determine if you connected polarity correct. ONLY CHANGE THE POLARITY ON 1 SPEAKER IF YOU ARE OUT OF PHASE! (doesn't matter which one)
PS the wires with the crimp connectors, just squeeze them with pliers to make a snug connection.