How do you tell which one is positive and negative?

[RARON455]

Hello I have a 98 trans am with the monsoon system in it and am putting speakers in, there are 4 speaker wires going to each door and 4 more going to each sail panel (which dont seem to be very loud) and more going to the rear hatch, I have a book on the car but none of the wiring is the right color, I read and have the monsoon wiring diagram on this site and my wire colors are not those colors, so since you dont have red/black you get colors like green and blue How do you know which ones are positive and negative, Is there a way to tell , I have a meter but dont know how you could test,, Any Help would be appreciated.....

[SteveCZ28]

the green and blue wires are seperate speakers....if i recall, youll have a white, and white/black striped. green, green/black striped. purple, purple/black striped. and gray, gray/black striped.....the solid colors are the positive, and the striped are negative