[randman1]

Under factory conditions, there is no correlation between the horn and starter circuit so I'm pretty confident that there is some aftermarket device in your car. If my guess is correct, look for a small "box" a little smaller than a pack of cigarettes and wires leading to the transaxle position switch. The wires will interrupt the starter wire which is a heavy gauge yellow wire going into the switch and a heavy gauge purple wire from the switch to the starter. It can be wired into either of the two wires. Sometimes the boxes are mounted on or near the dirver's side strut tower.