Does the horn work when you push the horn button?
Could be the horn button terminal at the turn signal connector is causing the relay to stay on but the horns should sound if that is happening.
Did you have the doors open when you connected the battery? The courtesy lights being on may have caused the spark at the battery, but if the relay clicks as soon as it is connected it sounds like the horn relay is energizing. Don't know if the 67 has the buzzer in the horn relay like the 68, it buzzes when the doors are open and the key is on.