If 'zapped' means the battery is going dead...? You have a circuit drawing current 24/7. Since you just wired several things up, it's a reasonable conclusion that you have either:
A. A connection on the wrong terminal and the power source is no longer 'switched', but is now 'constant on' or 'short'.
B. A positive circuit that is connected to 'ground' (short) and draining the battery.
C. Another problem unrelated to the new equipment...coincidence.
A voltmeter or other sensing device would be very useful here. Pigtail test lights are helpful, but often won't light up when you have a low-voltage constant drain or short.
Do the parts operate correctly when you turn them on? In other words, are the fogs fully bright or a little dim? Does the horn sound loud or a little weak? A dead short (bare wire touching ground) will cause either a lack of operation, or an intermittent operation if it's wiggling. A wrong connection will cause 'weak' operation usually, and may even provide operating current when the 'switch' is set to OFF.
Start by testing for current present at the device. The fogs should be 'cold' (no current) on both main power wires at the back of the lamps with the dash switch OFF. When ON these same wires should have a full 12v.
The horn is different. It should have a full 12v on in the hot wire at all times going to the horn button. There should be no current at the actual horn.
From there it's a process of working backwards through each terminal or wire route until you find the one that isn't cooperating.