help installing stereo on '87 ford taurus

I'm installing a head unit into a 1987 ford taurus.  The factory wires are already cut, no harness.  I've been trying to figure out the factory vehicle stereo wires (what is 12v, ground,...speaker wires etc.) With a tester I've managed to figure out 12v constant, battery (yellow wire)switch, and ground.  There are about five more wires that show current only when the switch is turned on.  I'm assuming these are the speaker wires (positive?).  Usually when I've connected stereos in other cars the speakers have matching wires like gray for positive and gray with black for negative.  I cannot find pairs for these factory wires.  Is there a special way I have to wire these?  Where can I find the negative?  There were one or two other wires that didn't show current at all.  I've tried connecting a negative speaker wire from the head unit to these wires and the positive pair to one of the factory wires that showed current. No sound.  The stereo will go on when I turn on the switch, I  just need to know how to hook up the speaker wires. Please help me.

https://www.the12volt.com/installbay/detail.asp?info=alarm&year=1986-88&make=Ford&model=Taurus&ID=17872&type=Stereo

right from 12volt it self