I think it is in the same position as in the 86-7 cars. It is halfway between the steering column and radio, right behind the instrument panel. There are two boxes plugged into the "convenience center". The big one (size of a pack of cigarettes) is the chime module. The small square relay next to it is the horn relay.
Your best bet, is to remove the cover under the dash, and come in from the bottom. You will probably have to work blind, and feel around until you find the two boxes together. To remove, wiggle while pulling the relay towards the front of the car. It will not be easy because you have no leverage. Happy hunting.