First the horn started blowing on its own, Then the starter cranks when you push the clutch in! wtf help!!!!!!!!
FWIW my horn staying on turned out to be melted wires at the bulkhead connector inside the car. The battery feed wire runs next to the horn wire and the battery feed wire started to melt and fused to it keeping the horn on. My fusible link went soon after and the problem was created at the ammeter.
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.