1997 Mercury Grand Marquis

Hi there everyone, Im really happy I found a site like this that carrys diagrams for free, more websites like this should be created. Now on to my question. The car is a 1997 Mercury Grand Marquis LS. The stock radio is a AM/FM casseste pictured here There is a amlifier in the trunk, so im assuming its a premium sound system. I went to best buy and the guy looked at my car and gave me 2 types of harness, one was the ford eliminator harness and the other one was something else but it wouldnt fit either. When I went to return the harness, he looked at the car and I told him the antenna was in the windsheild. Once I said that, a guy working on a car yelled "he has the car that you have to run new wires for everything. Im lost on this whole thing on what to do and I was wondering if you guys would be nice enough to help me. I have lots of pictures of the wires comming from the car and pictures of the stock radios inputs for them. I just dont know what to do in this situation, just wish it could be like my old radio where all i needed was a harness. I hope the pictures are usefull

Yeah thats the one that they gave me, and I also thought that it would fit, but it was just off slightly, plus the wires didnt line up with the pinouts on the car cable, there were on opposite sides