Simple motor question..

Yes im using the arduino and a motor driver... its just that
I installed both motors on my robot I connected positive(red) to (+) on battery, and the common(black) on to the (-) of the battery.

They are both installed same way.

Problem: 1 motor goes forward, the other goes backwards. No clue why, I doubled checked all connections!

I was just wondering if hurts the motor if you switch the wires