Bart,
I'm back. Please dumb this all down; way down for me. I get it that the wire coming out of the column is a "ground". What I cannot wrap my head around is...
what "powers up' the column and where?
I understand that the horn button is a switch which closes the circuit when you press the horn button and the horn beeps; but where does the power come from?
Thanks in advance pal.
Ed
Hi Ed, You don't need a dumbing down. You are no dummy that's for sure. I will explain the way I would like it explained to me. Without all the science. All I can give is the way I see it,
Not going to get into physics or electrons or neutrons or morons. Not going to discuss why we say electricity travels from positive to negative, but that really it is the opposite. It went too many years with that theory until science proved it wrong. DOES NOT MATTER when discussing simple DC truck wiring. I'm always going to say is flows from the battery positive to ground (neg).
Current flows from the battery to and thru "loads". Bulbs, motors, horn. On our trucks everything has a switch to turn the flow on and off. This flow must have a "return" path. (not talking home voltage, that's AC). On our trucks, the return wire is the whole truck and all it's current carrying metal.
The horn is sort of unique. Most switches on our trucks are letting positive voltage thru to a load and back thru the chassis. (Everything should pass thru a fuse of some sort). Lets call the way a horn diaphragm vibrates, "a load". It's not a bulb, not a motor, not a solenoid not a radio. I explained how it works. That too, it not important. It's a "load". I.E......something that uses the battery power.
Some older horns were wired with a wire from the battery/ammeter to the horn. Thru the load and back out another wire to the horn button. So where is the switch? Well, on this type horn we complete the entire horn circuit by closing the ground path at the horn button. This is the circuit style Carl is speaking of.
Then it was decided that closing a high draw "load" at the column was not good.
The horn is a good size amp draw. 10+ amps. 12 ga wire is used. Converting to 12V could affect draw. Switching a big draw at the button, with a disc and a plunger, wasn't the best switch. There also was a big voltage drop to the horn. The use of a remote relay supposedly shortened the wire. On the dual horns back then, they used a relay.
So on newer (about 1954) single horns used a relay. Solving several minor issues as above and eliminating an "always hot" horn terminal.
The relay has a low amp draw, electromagnetic coil inside. When you now ground the return path, you are just causing a magnet to close a set of big amp carrying contacts (the actual horn switch), which are also inside the relay. When that coil causes that switch to close, it connects voltage from the battery to the relay, thru those big contacts, out the relay to the horn. But then the horn "load" needs a return path with just that one hot wire going to it from the relay. So the horn is built with its return path thru it's own body, thru it's bolt, into the chassis and back to the battery which completes the circuit.........honks.
This electromagnetic coil get's power from the battery. The power input to the relay is split into two different circuits. One to the coil, thru the coil and out thru the relay's mounting screws into the chassis and back to the battery. This is very close to a starter solenoid. That is why it's called a switch by some vendors. Even called a relay. Ford used a separate starter relay
The other circuit is to the horn as explained.
Bottom line is the relay is the horn switch and the button is the relay switch.
ED, please answer what type of horn you have or how many terminals it has. So we can focus on YOUR horn hookup.
tclederman is correct (again), the later shapes were called Sea Shell, the older were call Klaxon. Delco-Remy got into the horn business in 1924 with the purchase of the Klaxon Horn Company in Newark, NJ. 
