1990 Mark 7 stero installation

can anyone tell me how to hook up my stero? i bought wiring harness to install with ,however the speaker adapter wont work with my factory wiring.my speaker wire runs to a black box in the trunk and then from there runs a gray cable that plugged into factory stero.i dont know if i explained this correctly, but anyone with a 1990 and up lincoln will know what im talking about.

the "black box" is you factory amplifier. From this amplifier a cable runs to the front of the car to the factory head-unit. I would either run new wiring to the factory speakers from the new head-unit or run all the speakers leads coming from the new head-unit to the location of the amp and splice them to the wires going to the speakers there. If you go with the second option use a batter to find each speaker's wire at the factory amp location. It would be easier to add an amp to the speakers in the car if you ever upgrade to an aftermarket amp though because you would have the new amp right where the wires going to your speakers are.