87 5.0 Stereo Wiring Diagram

well the easies way is to plug power direct to these pannel, ground to a good ground and there will be 4 pairs of wires that are coloured, thoese are the speakers, now if you really want the original power wires, a simple volt meter will make it easiy to find, constant power (for memory) will be active without the key, and accessory power will only be on while the key is on or in accessory mode, ground will be the only one left.
 
From my crutchfield instructions: Green left rear +, green/blk left rear -, violet right rear +, violet/blk right rear -, yellow 12v+ constant, red 12v+ switched, blk chassis ground, gray, right front +, gray/blk right front -, white left front +, white/blk left front -

Mike
 
there may be more wires if you have 6 speakers (dont know if they all do or not. my gt does). you could also go get one of the wiring kits from the parts store or walmart, etc. then use the diagram with it to figure it out, and return it if you want. i had to do this, but used the connectors for another car.

good luck. i hate it when people do that.