You've got a short somewhere, probably from tinkering with the wire harness under the dash. What were you doing under there? I suggested running your hot wire from the battery cable connector at the starter, where it's easy to reach. Now you're going to need to do some wire tracing and find where the short is. Try tracing the wire from the ammeter to the light switch, the headlight switch connections, and possibly the dimmer itself.
Jerry
