If you have power on the alternator lead and the fusible link unless something else is amiss you've completed the circuit through the ammeter. Do you have power to the ignition switch? You should as the black wire coming off the ammeter turns to a red wire in a splice and goes directly to the ignition switch. I'd start at the switch and work my way to the fuse block. With a '67 at least you can pull the switch out easily for trouble shooting.