The horns on theses have three wires.
one is positive, one is negative, the third is from the VSM. this is the signal wire to tell the horn to operate. Normally if you have a short or an open circuit it will show a code on the display, if not the horn driver in the VSM may be bad.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.