So far as blowing up the gauges it is easy to see how this happened. If the ammeter wire got to the common power supply to the gauges, yeh, poof. The path for that is ignition switch "run"---to the PC board connector---to the IVR for the gauges---out on traces to the individual gauges---through each gauge---and back out on the individual pc board terminals and off to the senders
So if the big battery/ ammeter wire contacted one of the points sending the regulated power to the gauges, it might have "killed" both of them.
There are ways to test them, "later." Get the thing to crank and run first, then the cluster