Engine stays running without key in ignition (and more!)

Hey folks, back from fighting fire in Oregon and I'm eager to get back under the hood! I'm going to pull the cluster so I can inspect the wires and connections, and replace the damaged gauge wires. I have two questions:

1) I read somewhere that it is wise to use wire that is specific to automotive applications, as it is made to withstand vibrations, etc. Is that true?

2) Second question is more of an update. I've started the car a couple times to move it in and out of the driveway since finding the melted wires, and while the dash light and ignition issues seem to be gone, now the ammeter moves with changing RPM. More specifically, the needle moves to the charge side (right) with increased RPM. I saw another thread here where the member was experiencing a similar issue, but I can't seem to find it. I'm still going to be checking connections, but I'm starting to suspect the alternator. Thoughts?