This was the other half of the statement that I was referring to...
The ammeter uses a shunt in the front harness to supply power to the ammeter, it is not connected in line with any power source. It wont affect anything with the truck running...If the gauge is fried, it will prevent power from getting to the ignition switch.
It's only getting a small sample of what is going on from the outside, that is why the gauge hardly moves... volt meters are much better for reading what the alternator is doing... hence the reason they went away from the amp gauge.
Now, if it was the idiot light for the alternator that was burned out then the alternator wouldn't work...
Shayne