If my girlfriend, 25, is on my car insurance, but she lets a friend borrow her car, should I be concerned?

My car is only two years old, but I’m already having problems with the alternator. Is this something that’s covered by my warranty?

I just bought a used car, but I test drove it during the daytime. Now that it’s dark out, I can’t figure out how to turn on the headlights. How do I turn on the low beams?

I have two cars. One I use for commuting and errands; the other I use far less. The annual mileage for the latter is about 3,000 miles and it's the most expensive car on my policy. It is financed and I'm wondering how I can get cheaper insurance on it since I don't drive it very often.