I'd pull the instrument cluster and look at the wires at the back of the Amp gauge. All the power goes through that gauge and if the nuts holding the wires on are the least bit loose, they start to arc and can produce enough heat to burn the ends off those 12 gauge wires. If that is where the problem is, it won't be hard to see the issue, anything less that a pristine connection on both wires indicates a problem. Gene