If you still owe money on your car and the warranty just expired on it but you do have full-coverage insurance and then the car has a huge mechanical break down how do you get it covered?

Sorry. Insurance covers accidental damage from accidents. It doesn't cover mechanical breakdown.

Hopefully you can get the car repaired and not find yourself paying on a "dead horse" but sometimes that is what happens. You need to protect your credit rating because someday you are going to want to make a major purchase such as a house or new car and if you have bad credit that is almost impossible.