On my original ignition switch (1951) there are three terminals. In the off position, all three are disconnected from one another. In the on postion, all three are connected together. I would think that you should bring your feed from the amp meter to one terminal and then take your switched loads from the other two. In the case of the turn signals, I powered mine from the unswitched side because I wanted the four way flashers to be available at all times. I used an inline fuse because the feed to the switch is completely unprotected.
