A couple other comments, I would suggest nothing between the battery and the ammeter except a fusible link. You show the power for wipers, horn, flasher connected to the battery side of the ammeter, meaning not only will they always be connected to power, but also the ammeter will indicate the current going to them from the alternator. Generally the ammeter only is to indicate charging current, not accessories current. If you are concerned with running that accessory current through the ignition switch, just add one or two relays to carry that power.
I don't know what horn you are using, most only have one power wire going to the horn and the horn relay switches that power. The horn is grounded at its attachment to the truck.
Are you going to add switches to light the dome light when you open the doors?
To each his own, I don't see anything that won't work, just a little unusual. Be sure to place a fusible link between the battery and the ammeter.
