[dsraven]

in order to make things easier to work on, try using a light instead of the horn. watch for the light to turn on instead of the horn blowing your ears out and annoying the neighbours.
disconnect the wire to the steering column, then power up the horn relay. common to have a problem with the steering column grounding the wire or a problem with the horn ring grounding.
check the relay for welded contacts
check the relay for power where it should be and grounds where they should be
it's just a horn, don't think too much into it. look at a wiring diagram if you are a bit lost on how it works, then probe each contact on the realy to figure out where the problem is