I'll try to help. There are different types of relays you will find, but most used will be (5) terminals. They are numbered: 30, 87, 87a, 85 and 86. You can set it up a number of ways but generally battery power is 30, and when energized power flows through to 87. When not energized, power dead heads at terminal 30. Terminals 85 and 86 are for the coil that moves the contact when powered up. You can power up the coil either way, 85 power and 86 ground or 85 ground and 86 power. When you do this you can provide power to any appliance and not damage the switch which turns it on, in this case the horn. When you press your horn button you provide a ground for the coil and this completes the circuit to energize the coil which in turn allows power from the battery (terminal 30) to any appliance (horn-light etc) through terminal 87. Hope this helps. I tried to attach a schematic of a relay but it was too big of a file. Let me know if you are still having trouble and I'll try harder to get one for you. David