I've had several battery drain issues with the alternator in my 2005 Mustang, which I believe is usually related to a failed diode. Is this still an issue with the alternator in the 5.0 models, as late as 2013? The only thing I've done to the car is install a stereo and speakers. I used all plug and play harnesses, but I also installed a bypass adapter along with it. I can't see the bypass causing an issue, especially since I installed pretty much the same radio and same bypass in my 2008 F-350.