I could help better if I knew what your vehicle is. Generally there is a wire from the starter solonoid where the battery cable connects to the ammeter. On some applications the horn feeds off from there.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.