in the old days mag switches etc had to be switched up for 'ON'. None of us were quite sure why.
When mag switches were mounted outside the cockpit on the side of the fuselage so the ground crew swinging the prop could see them a hand resting on them would turn them off, not on which is safer than a hand brushing over them and switching them, and the prop, live. It takes a more positive action to select a switch up than down so up - live down - safe is the better way of doing it.
How's that?