It's likely a dual horn setup, meaning there are two horns, one on each side of the center.
To access them, you'll likely need to:
1. Remove the front bumper. This involves removing a few screws or clips depending on the specific model.
2. Look behind the grille. The horns should be visible, attached to the metal frame of the car.
Remember, this information is based on typical horn placement and may vary depending on the specific model and year. It's always a good idea to refer to a repair manual or online resources specific to your 1980 Fiat Spider for accurate location and access instructions.