First and foremost - get a book and teach yourself about basic electricity. It will be invaluable throughout your life!
Secondly - get a wiring diagram for your car and the '99 if you can.
I just adapted the power seats out of an '87 TC to my '89 Stang. On my Stang there was already a connector under my manual seat for power seats. Check to see if you have one. If not, go to the junkyard and pull the seat wiring harness and switches from the '99. Also, get the connector that connects power to the wiring harness, on the floor, under the seat. Cut out that connector and about 6" of wire, so you have something to splice to. Basically, all your gonna have to do is run a wire for a hot lead from the fuse box and run one for ground, to the floorpan. This is where wiring diagrams come in. It will tell you the color of the power and ground wires and how many amps you will need for the fuse. It's not difficult, just take your time.