The horn relay is the squarish white plastic piece next to the "blue dingy thing" (aka convenience center). And BTW, the round silver piece is the hazard light flasher.
Anyway, you can test the horn by using a paperclip to connect dark green wire and the orange wire on the horn relay. This will send power directly to the horn, bypassing the relay and the steering wheel switch. The horn should sound when you do this. If not, then the horn is dead, or has a bad connection.
The horns are mounted to the front frame rails, on either side of the radiator, just behind the front impact beam. I can't remember, but I think the '88 Fiero only has one horn? If you remove the front wheels and detach the wheel well liners from the front fascia, you should be able to reach in there and get at the horns. The horns are grounded to the chassis via their mounting brackets. So if the mounting bolts rust up, it can block the flow of electricity. If the bolts are rusty, you can clean them up with a wire brush, and put some dialectric grease on them to prevent future rust.
You can also test the relay by grounding out the black wire that goes into the relay. Since you have the horn switch in the steering wheel disassembled, you can simply take that end of the black wire (it's the same wire) and touch it to some part of the steering column (wherever there's bare metal). That should activate the relay. If you listen closely, you should be able to hear the relay click (or hopefully the horn will sound).
Unfortunately, I can't tell you how to re-assemble the stock horn switch, because it's been so long since I had a stock steering wheel.
Oh, and last but not least, the horn runs off the "BAT" fuse. You should probably check the fuse, just in case.
[This message has been edited by Blacktree (edited 05-18-2010).]
