After a fire.....
First why not take a partial or complete load off the amp gauge and associate wiring. It's a extremely simple job.
Actually I was the one who said you don't have to, assuming everything is stock, and was about the ammeter, not the wiring.
The reasons with respect to the ammeter are:
a. It shouldn't be under much load. And it most certainly should not be under constant high load. If the needle pegs 40 amps, there is a problem. If it stays there or even near there, there is a big problem.
b. The ammeter is a useful tool. It reveals how much the battery is charging or discharging.
c. Many people think its something akin to an exploding device, hack their wiring, and make more problems than ever were there with the stock system. For Joe average with limited skils and tools its worth assessing whether its needed, especially if they are not willing to invest in doing well.
d. In your situation, the evidence we've seen so far is that there was a short to ground. This is something an ammeter in fact would show that a voltmeter would not. There's advantages to both instruments.
If you want to reroute the alternator and/or battery feeds, that's up to you. Done well, it will result in less resistance to flow, which is a good thing.
If you want to eliminate the ammeter, that also is up to you. I encourage you to install a voltmeter on a switched circuit if you do that.
Whatever you choose for rewiring, it would be prudent to:
First check for ground short in the main circuit - including the alternator.
Second, incorporate a fusible link on the battery feed.