64 Dart headlights, gauges, interior lights went out
You may have more than one problem. The head light switch sounds to be either wet or corroded. I had the same problem a few years back, you can still get them. Try disconnecting it just for laughs and see if it works for you.
ps. Get the color coded sheet from this guy on ebay. just enter in your make and model and search it will come up there like 20 bucks i got mine for the 64, hasn't proved wrong yet.