At the base of the steering wheel, there is a crescent plugin cluster of wires. That has all the steering wheel wires. The black is for the horn. test the wire there by apply ground (neg) to it. If it sounds there you will be good to the relay. If not there is a brake there along the way,

If that is good, make sure connection is tight there and try the button. If it don't work, we need to know what type of steering wheel you have so I know what button you have.