Headlights Turn Off While Driving problems of the 2008 Mazda CX-7

* engine issues when the a/c compressor locked up. This is a known issue in this make and model. This happened around 36k miles while I was driving on a freeway. We had to coast into the next exit. * engine knocking issues. They still persist and started around 50k miles. * engine resistance. Alongside the knocking there seems to be a good amount of resistance when taking your foot off of the pedal for acceleration. * they added a factory extension to the radio for the ipod. Ever since they installed this, the rest of the electrical components have been overloaded. - headlights go out frequently. This concerns me as my wife drives the car and I wouldn't want both to go out at the same time. - the battery won't hold a charge if not driven for a few days. The dealership acknowledged that the radio has a 'parasitic draw' on the battery causing these issues, but refuses to take responsibility for their installation. Their solution is to charge $800+ for a new head unit, which is outrageous since I never did anything to the factory head unit.