540i Intermittently Stops - Alternator or Ignition Switch?

Car: 2002 540i Problem: Since last Jan., the car intermittently stops and based on feedback I've gotten here, I've driven the car for 5 months to test the theories (e.g., visor test, turn radio and seat warmers on while driving) and they do appear to impact the car. Everytime, I drive the car without turning them on, it drives FINE. But the minute I pull visor down or put seat warmer on the car idles abnormally and cuts off. Based on research on the forum, it could be 1) ignition switch or 2)alternator. My husband says ignition switch was replaced a couple of years ago but not sure it was done right. Don't trust shop used. Any ideas where to start? Dealership said they don't know what problem is after charging us $350 for diagnostics! Just yesterday, I started car and it acts like it won't start initially and then starts. Oh and red battery light flashes when I start up and turn car off. HELP!