First the horn started blowing on its own, Then the starter cranks when you push the clutch in! wtf help!!!!!!!!
If I was going to throw darts, it would be steering column.
The right way is at this point is to disconnect the battery and test for cross wire short if there is nothing visually obvious.
Yours is not a short to ground, its a cross wire short. I don't know what instrument cluster or what mods have been made, etc but this should get you going.
'71 Horn relay is probably in the instrument harness as shown here. So unlike earlier cars, blowing the horn with the engine off will show on the ammeter. It also means the horn circuit is protected by the fusible link.
Not sure what, if any switch is on the clutch. If there is none- then the issue has to do with wires moving.
https://www.forabodiesonly.com/mopar/threads/short-to-ground-please-help.542352/#post-1974329760