I replaced my stock Audio 50 fiber optic head unit with a full screen nav unit since the CD and Cassette did not work. Then I realized that the CD player in it was shot and wouldn't even take a CD. I removed it and installed my original unit a couple days later the car died over night. I replaced the main and auxiliary battery and again the car died over night. Thinking there was something wrong with it, I removed it and reinstalled the full screen CD only unit and I no longer had the problem. I purchased another used Audio 50 unit and that works perfectly. That next day I get in the car and again it was completely dead. This seems so odd and frustrating!

 

I believe I have ruled out the head unit and the switch panel as the problem. I left them unplugged and there is still a complete battery drain over a 8 hour period.