Horn electrix…

I've never understood much about electrics exept easy plus & minus without relays & such & now I have to re-wire the bit under the dashboard on my -56 New Yorker & I've looked at the diagrams & the ones I've found all shows 4 points on the relay but mine only have 3... & it seems that the horn button grounds & the horns grounds too, is that right?
Author: Glider