Horn gone crazy

[capeclassics]

The other day I hit the horn and nothing,zero,zilch,nada.......
Put a new horn relay in and the horn just keeps blaring away non-stop!!
How to troubleshoot?
Thanks

[DGrant09]

It is my understanding that the horn button on the steering wheel applies a ground to the horn relay when the horn is pressed. The relay then closes and sends power to the horn(s).
I would try to unplug the wire from the horn button at the relay and see if there is a constant ground on the wire. Is so, I would probably look at the horn button mechanism to see if that has stuck. If that's good, I would suspect the wire from the button has shorted to something.
When the horn wire is removed from the relay and 12v connected to the relay, does the horn still sound? If so, check the connection(s) on the relay for shorts and correct pin location, then check the relay.
We figured ours out this way..

[capeclassics]

OK,where is the horn ground wire on a 70 F-100 360 automatic?

[DGrant09]

On our 72 we have the horn pad vs. the round button, not sure what is on a 70. Behind the horn pad we have a wire coming through the steering wheel column and attaches to the horn pad, and then another attaching the horn pad to the steering wheel column itself. On the turn signal switch base there is a small spring assembly that has a small metal pin stuck into on end (this end points to the steering wheel). When the horn pad is pressed it contacts the metal pin which completes a ground circuit from the steering wheel column to the horn wire that passes through the steering column and is connected to the horn relay.
Our horn relay is mounted next to the starter relay.
On the horn relay we have three wires. One from the starter relay, one going to the horns themselves, and then the ground wire (blue and white in ours) from the horn pad.
We checked the wire from the column (blue and white) for a good ground when the horn was pressed. I did not have a good ground so we removed the horn pad and found our spring assembly was missing. Once we installed it we had a good ground.
The wire from the starter relay should have 12v continuously. If it is there, I removed the ground wire from the horn pad at the horn relay and ran a jumper to to the relay from a known good ground. The horn (s) should sound as soon as it is grounded. If it does not, as one of mine did not, I then jumped 12v directly from the battery to each horn and we figured out which one was bad. If they work and there are no broken wires then I'd look at a new horn relay.
Here is a basic horn circuit from second chance garage dot com ,I removed the ignition switch from the picture.

Hope this makes some sense for you