setting up 6x9s and deck in chevy caprice classic need help!!!!?

[Luke S]

ok so im putting in a new head unit and 6x9s in my 1976 caprice classic and there are a couple problems. first there were multiple harnesses plugging into the old atrax player so ive had to do some work to find which wires go where. i think ive figured it out. but for the back speaker there are only two wires that are running from the front of the car to the back 6x9s.... its a blue and brown wire. the blue wire runs along the left side of the car and the brown the right side. but the kenwood deck i bought has a positive and negative wire for each speaker.. but the back 6x9s only have one wire to each like i said. i was wondering if i can just figure out which wire running to the speakers is positive and which one is negative and then just take one positive wire from the deck for the speakers and one negative wire and leave the other two positive and negative wires i didn't use open.. example. if the blue wire going to the 6x9 speakers is positive and the brown wire is negative could i take the left rear positive wire from the deck and wire it to the blue one.. then the right rear negative wire from the deck to the brown wire then just leave the left over positive and negative wires alone?? this is my first time putting a system in and its on a older car too so its proving to be a little hard but i think with some good help i can do it with a breeze. any informative input is appreciated