you have 2 horns' both close to the head litghts on left and right side
horns are usually located near the grill area in front of the car.
The horn for the 1990 Mazda Protege is located near the right turn signal at the front of the car. To the left of the radiator when your looking at the engine with the hood up.
Have your Mazda dealer parts department print out a picture of the relays location for you. They will do this if you ask them.
It's difficult to find but easy to get to (if that makes sence). Just take off the front grill. There are two screws inside the hood. pop that off, and the horn should be right there.
Open hood and disconnect the wire from the horn itself located under right front fender.
in the stearing wheel
It is important to know where the parts are within a car. The horn relay in a 1993 Mazda Protege is found in the cars fuse box.
The horn is located on the front passenger side of the car. if you remove the front passenger headlight you will be able to see it from there
behind the plastic grill on the front.
The horn fuse is the same as the stop lamp fuse
The owners manual should have a fuse box diagram. If you don't have one, try MOTORLIT.COM
I have a 1993 Mazda Protege LX and I was told that there is no relay for the horn, there is a horn switch inside your steering wheel. that might help