Usually, providing the contacts are good which you verified by testing for power with your test light. Bad contacts could also show voltage but lack the current to allow the horns to work, so swapping them with a known working relay was a good idea. At this point I would unmount the horns and hook them straight up to the battery, casing of the horns gets the negative and one wire terminal gets positive. No blow and you know your horns are bad.And a clicking relay is a good relay?
Ok. Will try that later tonyt......BMW horns louder?