Thanks for all the good ideas from everyone. As for the alternator, it was professionally rebuilt with new brushes so I think it might be okay. I had an extremely weird failure mode in my Duster last year that was a bit similar to this. The high beam headlights would cut out at night, leaving me going down the dark highway with NO LIGHTS. Very distressing. I instantly hit the floor dimmer switch to cut in the low beams, and the headlights came back on. This happened several times, so I pulled over. As I did, I had an entire electrical failure of the car. Everything went absolutely dead. Nothing. Opened the hood, couldn't find any problems. Five minutes later, I heard a click and the interior lights came back on. I was able to restart and drive the car with the headlights off the rest of the way. Replaced the floor dimmer switch and never again had that problem. It would appear that the main power for the car is routed in through the headlight switch, and that some sort of circuit breaker in the headlight switch cooled enough to reset itself and restore power to the car. Somehow, the dimmer switch was shorting something and overloading this circuit breaker.
