Moomba factory speaker wire...What is going on her

So i was running my speaker wire from my cabin speakers to my amp. What i always thought and went by is + is the copper wire - is the silver wire. I almost positive speakers to an amp matter what is + and -. What i noticed is all the speakers are right but the wire runs to a factory plug and then into the back of the head unit and they are all different + going to a - nothing is the same. Correct me if i am wrong but it does matter the i have all the + wires from the speakers to the + inputs of the amp and same with the -