It's baaaack! HELP

You usually (after disconnecting the battery) loosen the steering column and let it hang down a bit. A bodies used a metal clip similar to the one in your trunk for the wiring to the tail lights. It is located just above the speedometer cable just at the back of the instrument panel and it holds your under dash wiring, that is probably what is holding you up. Be careful when you are removing your instrument cluster, you should be able to get it out far enough to disconnect the amp meter after that it will come out after you CAREFULLY unplug the wiring from the board/boards.
If I were you I would only get your cluster out far enough to remove and clean up the connections of the amp meter and reconnect them securely to eliminate that from the equation. I seriously doubt that your gauge will cause intermittent problems like you are having. But the connections are another story, I found mine loose on many A-Bodies I have owned.