Rick, I used the Hella parts and figured I might mention something.
They are sensitive to ground. You must have a good ground.
Mine was simple, I powered one side of the relay and passed the other side to the horn button on the column. Then I powered the contact in the relay. the other side of the relay I ran to the horns. Then one side is grounded and the other side is powered when the button is pressed.
One more thing, make sure you bolt them down well.
