horn activated starter kill

if you wired it exactly as in the diagram, your horn should not sound at all until you hit the starter. Sounds like your modification using 87A is the problem. The sequence you need to follow is: 1) Switch the ignition on but don't try starting 2) press and release your horn to latch in the two upper relays, which allows the left upper relay to pass the key side of starter to the motor side of starter. If you don't hit the horn, the upper left relay is off, and the starter signal is disconnected, preventing start. 3) hit the starter, which latches in the bottom two relays. At this point, the horn relay (+) is connected to horn positive, allowing the horn to sound if you hit the horn again. The bottom right relay is latched so the horn will continue working, until the car is turned off again. You may have to check into how you inverted the horn signal and see if it does what it has to in the diagram. The line from the horn relay (+) has to go to 12V when you hit the horn, and the line going to the horn should sound the horn when 12V is applied to it. If you're using the negative side of the horn switch it won't work.