[DeTomaso] Newby here

[John Buckman]

Brian,

The horn is activated by pushing in on the end of the turn signal stalk, as you noted.

There is a horn relay that is located with the other relays and the turn signal flasher.

The horn relay is fed (via a red wire) from fuse #7.  The load wire from the relay goes to the horns, via a white wire.

There is a brown wire that goes from the relay’s coil to the turn signal stalk.  The relay’s coil circuit is completed (to ground) when the stalk is pushed in.  

You should be able to hear the relay “click” when the stalk is pushed in.  The key does not need to be on.  

The above pertains to the original wiring on ’71-'74 Panteras.

John