I think it might be that the connector to the horn has come off (this is not that unusual). If the interior lights are connected in series with the horn, they would go as well. The horn connector is found sometimes in the horn pad, or in the dash just under the instruments, or within the steering column cover.

Smack the jandy box about 1/3 of the way up from the bottom with your fist. If the pump stops, the relay needs to be replaced. If it doesn't stop smack it harder. If it doesn't stop then, you might need a new control board.

You wired it wrong. Please give us some details of what you did. If you conencted it to the same two wires as the old fixture then it should work. It you tried to FIX a problem you thought you saw when black and white wires were connected together then you messed it up.

I'm betting the new switches are not physically the same as the old ones. On 3b make sure the Black wire from the 2-conductor cable is connected to the Common terminal of the 3-way switch. The replacement and original may not be physically identical though they may be electrically equivalent. On 3a, same thing - make sure the black wire is connected to the Common terminal. It should be marked "Comm" or the screw will be a different color. Remove the 4-way and wire nut the wires together, red to red and white to white. This will enable you to get the circuit working with just the 3-way switches. Once that is done you can work on re-installing the 4-way correctly by following the wiring diagram that comes with it. BE CAREFUL - you do not show the complete circuit diagram and I am making assumptions on what the wires are based on limited information. Double check that the wires truly are connected as shown.