Horn not working

[71newp]

I have a 1976 Cordoba, One morning when I started it, the horn went on by itself, then over a period of 1-2 seconds faded out. I have determined that it is blowing the fuse (according to the flow chart in the FSM) due to a bad ground. When I replace the fuse I can hear the horn relay clicking (a new one and the old one) a few times until the fuse goes. The horn worked and the fuse did not blow when I had a properly grounded test light in the female clip that attaches to one of the horns. I can not tell by looking at the wiring diagram where it is grounded. Please help...this issue is harshing my mellow!
Tim

 

[Shorthorse]

The horns ground is its body. It is grounded by being bolted to the car. Remove the horn and clean both surfaces where it is bolted on.

 

[Lionized]

The horns ground is its body. It is grounded by being bolted to the car. Remove the horn and clean both surfaces where it is bolted on.

Add a smear of dielectric grease before bolting them back on.