quick question about cd player

I just recently bought a 93 LX Hatchback 5.0, and it came with the stock deck. The first thing I wanted to do was get rid of that, so I went to a local vendor and bought a wiring kit to hook up my cd player. Sure enough, even though it said "made for ford 85-2004" or whatever, the connectors were different. I took it back down there and all he said was "Ford is really weird, sometimes these wiring kits don't hook up, in that case, you have to hard wire it to the existing wires, and run your own speaker wires to the speakers." Is this true? Is it really that hard to hook up a cd player in my mustang?

Just wire it up, the speaker wire are already ran, all you have to do is ohm them out, if you do not have a multimeter, you can use a AA battery on the wires, to find out which speaker goes to which wire. When the battery is hooked up, the speaker with produce a hum.

I want to be able to hook the stock deck up at some point, say when I sell it. Are there any available harnesses? I don't wanna go cuttin into all that stuff.

Woah hold up.
93's are a bit different. I think they came stock with a premium sound system.
There is an amp hooked up to them and you have to bypass it to get to the speakers. So you could easily do that, but you will have to run three wires for the main part. They come off your CD player as followed.
Red - accessory.....turns on when your ignition turns on and off as well. Wire to like an open fuse slot or find one off the radio's existing wiring.
Yellow - main power wire, it keeps the power constant to the radio so that it will keep your presets and everything stored in. Must hook up to a constant power source, make sure there is a fusible link in there. (ex....lighter or something for the car.)
Black - black of course is our ground wire.

If I am correct some of the plugs should be the same atleast to the power side of it. The one that its different should be for the speakers and that is where your trouble begins, becuase it goes into the amp. I disconnected them at the plug into the speakers and then ran my own wire. This way all I had to do was plug them back up and then put the stock deck back in when I wanted to.