http://www.247motorsports.com/downloads/90FSM.zip
First download the above service manual. It will have the wiring diagram with all the wire colors. It is in the "system_w" section on page 7 or 8. Hope you are familiar with how to read wiring diagrams.
If the old harnesses have been cut off, you will either need to get new stock harnesses and splice them on so you can have something to plug the harness from the radio in, or direct splice every single wire from the radio to the car.