Having the horn disconnected won't hurt your other speakers at all, so ignore that comment.
Some folks go into the L-pad and pull out the car bulb-type fuse to disconnect it because turning it off all the way can make the L-pad overheat and melt connectors. So they are disconnecting it by pulling that bulb-fuse. Lots of folks like the sound better without the horn, but it really is just personal preference. From discussions here I would say a LOT of folks turn that tweeter control on the L-pad just one notch above off.
I still would search for that wiring diagram to make sure the rest of the speakers are hooked up correctly, but don't worry about the horn disconnect damaging your speaker. That's a non-issue.