Randall has bailed me out all the time with electrical stuff, and I am far of being an expert, so I will try and make a wild theory here.
When I think of the amp gauge, I think of how the gauge is in line of a hot wire and not across 2 wires like a volt meter. Which I guess a fuel gauge basically is--- a volt meter with hot and ground with resistance in the center. Having said all that, the 2 gauges are next to each other so maybe something happened, but yes not a direct correlation. If the glove box is out of your car or you do not have a heater, looking around the back of the dash is easier and that is where I would start. I would unhook one of the battery cables or loosen it, so I can unhook and re-hook, but start with it unhooked and look and see if something fell.